V4L/DVB (11623): cx18: Verify cx18-av-core digitizer firmware loads correctly

Add code to verify the cx18-av-core digitizer firmware loads correctly.  The
verification function reads back and compares the firmware bytes loaded
into the A/V core.  The result of the verification is only used to log a
message in the system log.

This change was prompted by users with multiple card setups that have problems
with broadcast audio decoding the first time the cx18 module is loaded.

Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>