media: allegro: set num_ref_idx using response of configured channels

The firmware decides how many reference frames shall be used und returns
this information via the config blob. In order to set the number of
reference frames in the PPS, the driver has to read these values from
the config blob after the channel has been created in the firmware.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>