V4L/DVB (10938): em28xx: Prevent general protection fault on rmmod

The removal of the timer which polls the infrared input is racy.
Replacing the timer with a delayed work solves the problem.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>