[media] ir-nec-decoder: fix repeat key issue

Fixing the problem with NEC protocol and repeating keys under the following
circumstances. The problem occurs when there is a repeat code without
properly decoded scancode. This leads to repeat the wrong (last decoded)
scancode.

An example from real life:
I am pressing volume down, then several minutes later i am pressing
volume up, but the real scancode is wrongly decoded and only a repeat
event is emitted, so as a result volume is going down while i am holding
volume up button.

The patch fixes above problem using rc_keyup timeout (as pointed by Mauro).
It just prevents key repeats if they appear after rc_keyup.

Signed-off-by: Mariusz Białończyk <manio@skyboo.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>