[media] af9015: enhance RC

[media] af9015: enhance RC

Patch from Ian Armstrong.

I've encountered a couple of problems with the current af9015 driver as
supplied with the 2.6.37 kernel, that the attached patch appears to fix. (I've
generated this patch against the current v4l-dvb git).

Some key-presses are lost. A key-press is only generated upon 'valid' data
(buf[14] == (u8) ~buf[15]), but the buffer is wiped before this check.
Sometimes the 15th byte has not been set at the time of read, so the data
isn't valid & ignored. On the next poll the 15th byte has been set, but the
rest of the data was wiped previously, so the data is still invalid & the key
is lost.

Weird repeat error, where an old key press is sometimes repeated in error. ie.
button sequence '1 (pause) 2 (pause) 3 (pause) 4' generates output like '1
(pause) 2 (pause) 23 (pause) 4'. The current driver zeroes the data for the
key pushed, but sometimes this data is already zero but with other bytes set
suggesting a repeat code. This results in the last key being incorrectly
repeated.

This patch attempts to reduce the risk of a missed key-press & also stop the
random repeat of an old key-press when a new key is pressed.

Signed-off-by: Ian Armstrong <ian@iarmst.demon.co.uk>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>