[media] au8522: Properly set default brightness

The chip's default value for the brightness didn't match what we were sending
back in the queryctrl ioctl(), so if the application actually set the
brightness to the "default", it would actually end up being way too bright.

This work was sponsored by GetWellNetwork Inc.

Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>