staging: vt6655: device_main: Replace explicit NULL comparison

Replace NULL comparison to resolve checkpatch issue.
- x == NULL => !x

Signed-off-by: Namrata A Shettar <namrataashettar@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vt6655/device_main.c

@@ -735,7 +735,7 @@ static bool device_alloc_rx_buf(struct vnt_private *priv,
 	struct vnt_rd_info *rd_info = rd->rd_info;
 
 	rd_info->skb = dev_alloc_skb((int)priv->rx_buf_sz);
-	if (rd_info->skb == NULL)
+	if (!rd_info->skb)
 		return false;
 
 	rd_info->skb_dma =