Staging: rtl8712: rtl8712_xmit: Use !x instead of x == NULL

Use !x instead of x == NULL. This patch was found by checkpatch.
Signed-off-by: Sandhya Bankar <bankarsandhya512@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8712/rtl8712_xmit.c

@@ -629,7 +629,7 @@ int r8712_xmitframe_complete(struct _adapter *padapter,
 
 	phwxmits = pxmitpriv->hwxmits;
 	hwentry = pxmitpriv->hwxmit_entry;
-	if (pxmitbuf == NULL) {
+	if (!pxmitbuf) {
 		pxmitbuf = r8712_alloc_xmitbuf(pxmitpriv);
 		if (!pxmitbuf)
 			return false;