[media] m920x: avoid repeating RC state parsing at each keycode

Parsing the RC press state is invariant wrt. the keycode, take it out of
the keycode scanning loop.

Signed-off-by: Antonio Ospite <ospite@studenti.unina.it>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>