[media] mb86a20s: change AGC tuning parameters

Use the AGC settings present on a newer device.
The initial settings were taken from one of the first devices with
mb86a20s, and there are several reports that this is not working
properly on some places.
So, instead of keeping using it, get the parameters taken from a
newer device. Tests are welcomed.
Tested also with cx231xx PixelView SBTVD Hybrid with no regressions
noticed so far.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>