mn88473: fix chip id check on probe

commit d930b5b5 upstream.

A register used to identify chip during probe was overwritten during
firmware download and due to that later probe's for warm chip were
failing. Detect chip from the another register, which is located on
different register bank 2.

Fixes: 7908fad9 ("[media] mn88473: finalize driver")

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>