V4L/DVB: IR: nec decoder: fix repeat

Repeat space is 4 units, not 8.
Current code would never trigger a repeat.

However that isn't true for NECX, so repeat there
must be handled differently.

Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
Reviewed-by: Andy Walls <awalls@md.metrocast.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>