media: adv7180: Move state mutex handling outside init_device()

media: adv7180: Move state mutex handling outside init_device()

Future rework to get rid of .s_power requires the state mutex to be
held for multiple operations where initializing the device is one of
them.

Move lock handling outside init_device() but enforce the lock is held
with a lockdep_assert_held().

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>