TTY: pdc_cons, fix racy tty test

The tty->count test in the timer was racy. Let's remove the test and
properly delete the timer and wait for the body to finish using _sync
version of del_timer.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Kyle McMartin <kyle@mcmartin.ca>
Cc: Helge Deller <deller@gmx.de>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>