qtnfmac: fix error handling in control path

This patch fixes the following warnings:

- smatch
drivers/net/wireless/quantenna/qtnfmac/commands.c:132 qtnf_cmd_send_with_reply() warn: variable dereferenced before check 'resp' (see line 117)
drivers/net/wireless/quantenna/qtnfmac/commands.c:716 qtnf_cmd_get_sta_info() error: uninitialized symbol 'var_resp_len'.
drivers/net/wireless/quantenna/qtnfmac/commands.c:1668 qtnf_cmd_get_mac_info() error: uninitialized symbol 'var_data_len'.
drivers/net/wireless/quantenna/qtnfmac/commands.c:1697 qtnf_cmd_get_hw_info() error: uninitialized symbol 'info_len'.
drivers/net/wireless/quantenna/qtnfmac/commands.c:1753 qtnf_cmd_band_info_get() error: uninitialized symbol 'info_len'.
drivers/net/wireless/quantenna/qtnfmac/commands.c:1782 qtnf_cmd_send_get_phy_params() error: uninitialized symbol 'response_size'.
drivers/net/wireless/quantenna/qtnfmac/commands.c:2438 qtnf_cmd_get_chan_stats() error: uninitialized symbol 'var_data_len'.

- gcc-8.2.1
drivers/net/wireless/quantenna/qtnfmac/commands.c: In function 'qtnf_cmd_send_with_reply':
drivers/net/wireless/quantenna/qtnfmac/commands.c:133:54: error: 'resp' may be used uninitialized in this function [-Werror=maybe-uninitialized]

Reported-by: Dan Carpenter <[e-mail]>
Reported-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Sergey Matyukevich <[e-mail]>
Signed-off-by: Kalle Valo <[e-mail]>

drivers/net/wireless/quantenna/qtnfmac/commands.c

···
 				    size_t *var_resp_size)
 {
 	struct qlink_cmd *cmd;
-	const struct qlink_resp *resp;
+	struct qlink_resp *resp = NULL;
 	struct sk_buff *resp_skb = NULL;
 	u16 cmd_id;
 	u8 mac_id;
···
 	if (ret)
 		goto out;
 
-	resp = (const struct qlink_resp *)resp_skb->data;
+	if (WARN_ON(!resp_skb || !resp_skb->data)) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	resp = (struct qlink_resp *)resp_skb->data;
 	ret = qtnf_cmd_check_reply_header(resp, cmd_id, mac_id, vif_id,
 					  const_resp_size);
 	if (ret)
···
 	struct sk_buff *cmd_skb, *resp_skb = NULL;
 	struct qlink_cmd_get_sta_info *cmd;
 	const struct qlink_resp_get_sta_info *resp;
-	size_t var_resp_len;
+	size_t var_resp_len = 0;
 	int ret = 0;
 
 	cmd_skb = qtnf_cmd_alloc_new_cmdskb(vif->mac->macid, vif->vifid,
···
 {
 	struct sk_buff *cmd_skb, *resp_skb = NULL;
 	const struct qlink_resp_get_mac_info *resp;
-	size_t var_data_len;
+	size_t var_data_len = 0;
 	int ret = 0;
 
 	cmd_skb = qtnf_cmd_alloc_new_cmdskb(mac->macid, QLINK_VIFID_RSVD,
···
 {
 	struct sk_buff *cmd_skb, *resp_skb = NULL;
 	const struct qlink_resp_get_hw_info *resp;
+	size_t info_len = 0;
 	int ret = 0;
-	size_t info_len;
 
 	cmd_skb = qtnf_cmd_alloc_new_cmdskb(QLINK_MACID_RSVD, QLINK_VIFID_RSVD,
 					    QLINK_CMD_GET_HW_INFO,
···
 			   struct ieee80211_supported_band *band)
 {
 	struct sk_buff *cmd_skb, *resp_skb = NULL;
-	size_t info_len;
 	struct qlink_cmd_band_info_get *cmd;
 	struct qlink_resp_band_info_get *resp;
+	size_t info_len = 0;
 	int ret = 0;
 	u8 qband;
 
···
 int qtnf_cmd_send_get_phy_params(struct qtnf_wmac *mac)
 {
 	struct sk_buff *cmd_skb, *resp_skb = NULL;
-	size_t response_size;
 	struct qlink_resp_phy_params *resp;
+	size_t response_size = 0;
 	int ret = 0;
 
 	cmd_skb = qtnf_cmd_alloc_new_cmdskb(mac->macid, 0,
···
 	struct sk_buff *cmd_skb, *resp_skb = NULL;
 	struct qlink_cmd_get_chan_stats *cmd;
 	struct qlink_resp_get_chan_stats *resp;
-	size_t var_data_len;
+	size_t var_data_len = 0;
 	int ret = 0;
 
 	cmd_skb = qtnf_cmd_alloc_new_cmdskb(mac->macid, QLINK_VIFID_RSVD,