TTY: disable debugging warning

We added a warning to flush_to_ldisc to report cases when it is called
with a NULL tty. It was for debugging purposes and it lead to a
patchset from Peter Hurley. The patchset however did not make it to
3.9, so disable the warning now to not disturb people.

We can re-add it when the series is in and we are hunting for another
bugs.
Reported-by: NDavid Miller <davem@davemloft.net>
Cc: stable <stable@vger.kernel.org>   # 3.8
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/tty_buffer.c

@@ -425,7 +425,7 @@ static void flush_to_ldisc(struct work_struct *work)
 	struct tty_ldisc *disc;
 
 	tty = port->itty;
-	if (WARN_RATELIMIT(tty == NULL, "tty is NULL\n"))
+	if (tty == NULL)
 		return;
 
 	disc = tty_ldisc_ref(tty);