V4L/DVB (13001): Key filter for BeholdTV cards.

When fast push-pull button of remote control we can received incorrect
key code 0x00. Key information from IR decoder has ID of remote control 2 bytes,
byte of key code and byte of mirror key code.
Correct data
0x86 0x6B 0x00 0xFF

Wrong data
0x86 0x6B 0x00 0x00

This patch added additional test of mirror byte for filtering.

Signed-off-by: Beholder Intl. Ltd. Dmitry Belimov <d.belimov@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>