wifi: rsi: Slightly simplify rsi_set_channel()

There is no point in allocating 'skb' and then freeing it if !channel.

Make the sanity check first to slightly simplify the code.

Signed-off-by: Christophe JAILLET <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Signed-off-by: Kalle Valo <[e-mail]>
Link: https://lore.kernel.org/r/29bf0296bd[e-mail]

drivers/net/wireless/rsi/rsi_91x_mgmt.c

···
 	rsi_dbg(MGMT_TX_ZONE,
 		"%s: Sending scan req frame\n", __func__);
 
+	if (!channel)
+		return 0;
+
 	skb = dev_alloc_skb(frame_len);
 	if (!skb) {
 		rsi_dbg(ERR_ZONE, "%s: Failed in allocation of skb\n",
···
 		return -ENOMEM;
 	}
 
-	if (!channel) {
-		dev_kfree_skb(skb);
-		return 0;
-	}
 	memset(skb->data, 0, frame_len);
 	chan_cfg = (struct rsi_chan_config *)skb->data;