ath9k: cleanup: remove unneeded null check

We dereference "wmi" on the line before and also when we initialize "ah".
This check has always been after a dereference since the first commit a
couple months ago.  Looking through the code, it looks like "wmi" can't
actually be null here so I just removed the check.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Sujith <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/wmi.c

@@ -279,9 +279,6 @@ int ath9k_wmi_cmd(struct wmi *wmi, enum wmi_cmd_id cmd_id,
 	if (wmi->drv_priv->op_flags & OP_UNPLUGGED)
 		return 0;
 
-	if (!wmi)
-		return -EINVAL;
-
 	skb = alloc_skb(headroom + cmd_len, GFP_ATOMIC);
 	if (!skb)
 		return -ENOMEM;