media: coda: add lockdep asserts

coda_command_sync, coda_hw_reset, and __coda_start_decoding
all expect to be called under the coda_mutex device lock.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>