wifi: cw1200: cleanup the code a bit

Delete if NULL check before dev_kfree_skb call.
This change is to cleanup the code a bit.
Signed-off-by: Bernard Zhao <bernard@vivo.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220517014136.410450-1-bernard@vivo.com

drivers/net/wireless/st/cw1200/bh.c

@@ -327,18 +327,12 @@ static int cw1200_bh_rx_helper(struct cw1200_common *priv,
 	if (WARN_ON(wsm_handle_rx(priv, wsm_id, wsm, &skb_rx)))
 		goto err;
 
-	if (skb_rx) {
-		dev_kfree_skb(skb_rx);
-		skb_rx = NULL;
-	}
+	dev_kfree_skb(skb_rx);
 
 	return 0;
 
 err:
-	if (skb_rx) {
-		dev_kfree_skb(skb_rx);
-		skb_rx = NULL;
-	}
+	dev_kfree_skb(skb_rx);
 	return -1;
 }