ath6kl: fix return value in ath6kl_wmi_set_pvb_cmd

When building with W=1, we got one warning as belows:
drivers/net/wireless/ath/ath6kl/wmi.c:3509:6: warning: variable ‘ret’
set but not used [-Wunused-but-set-variable]

At the end of ath6kl_wmi_set_pvb_cmd, it is returned by 0 regardless of
return value of ath6kl_wmi_cmd_send.
This patch fixes return value from 0 to ret that has result of
ath6kl_wmi_cmd_send execution.

Signed-off-by: Chaehyun Lim <[e-mail]>
Signed-off-by: Kalle Valo <[e-mail]>

drivers/net/wireless/ath/ath6kl/wmi.c

···
 	ret = ath6kl_wmi_cmd_send(wmi, if_idx, skb, WMI_AP_SET_PVB_CMDID,
 				  NO_SYNC_WMIFLAG);
 
-	return 0;
+	return ret;
 }
 
 int ath6kl_wmi_set_rx_frame_format_cmd(struct wmi *wmi, u8 if_idx,