[PATCH] tty_io.c balance tty_ldisc_ref()

tty_ldisc_deref() should only be called when tty_ldisc_ref() succeeds
otherwise it triggers a BUG().  There's already a function
tty_ldisc_flush() that flushes properly.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>