media: mtk-cir: reduce message end to fix nec repeats

The ir receiver generates an interrupt with the IR data, once a space of
at least ok_count is has been seen. Currently this is about 110ms; when
holding down a button on a nec remote, no such space is seen until the
button is released. This means nothing happens until you release the
button.

The sample rate is fixed at 46us, so the maximum space that can be
encoded is about 12ms. So, the set ok_count above that at 23ms.

Cc: Sean Wang <sean.wang@mediatek.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>