Bluetooth: btuart_cs: Comparison to NULL re-written

NOT NULL comparison modified to be readable, reported
by checkpatch.

Signed-off-by: Prasanna Karthik <mkarthi3@visteon.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/bluetooth/btuart_cs.c

@@ -188,7 +188,7 @@ static void btuart_receive(struct btuart_info *info)
 		info->hdev->stat.byte_rx++;
 
 		/* Allocate packet */
-		if (info->rx_skb == NULL) {
+		if (!info->rx_skb) {
 			info->rx_state = RECV_WAIT_PACKET_TYPE;
 			info->rx_count = 0;
 			info->rx_skb = bt_skb_alloc(HCI_MAX_FRAME_SIZE, GFP_ATOMIC);