Char: mxser, 0 to NULL in pointer

Don't test a pointer against 0. Use NULL instead.
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Reviewed-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/char/mxser_new.c

@@ -2153,7 +2153,7 @@ static void mxser_transmit_chars(struct mxser_port *port)
 		return;
 	}
 
-	if (port->xmit_buf == 0)
+	if (port->xmit_buf == NULL)
 		return;
 
 	if ((port->xmit_cnt <= 0) || port->tty->stopped ||