[media] fintek-cir: make suspend with active IR more reliable

There was a missing lock in fintek_suspend. Without the lock, its
possible the system will be in the middle of receiving IR (draining the
RX buffer) when we try to disable CIR interrupts.

Signed-off-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>