Staging: rtl8188eu: hal: rtl8188eu_xmit.c: Remove explicit NULL comparison

Remove explicit NULL comparison and write it in its simpler form.
Replacement done with coccinelle:

@replace_rule@
expression e;
@@

-e == NULL
+ !e

Signed-off-by: Shraddha Barke <shraddha.6596@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/hal/rtl8188eu_xmit.c

@@ -649,7 +649,7 @@ static s32 pre_xmitframe(struct adapter *adapt, struct xmit_frame *pxmitframe)
 		goto enqueue;
 
 	pxmitbuf = rtw_alloc_xmitbuf(pxmitpriv);
-	if (pxmitbuf == NULL)
+	if (!pxmitbuf)
 		goto enqueue;
 
 	spin_unlock_bh(&pxmitpriv->lock);