TTY: move pgrp killing

Move it to the only branch where tty_pgrp may be set. This is only a
cleanup which allows having tty_pgrp defined at that place.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>