[media] saa7134: merge saa7134_card_ir->timer and saa7134_card_ir->timer_end

Both timers are used for a similar purpose. Merging them allows for some
minor simplifications.

Signed-off-by: David Härdeman <david@hardeman.nu>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>