media: coda: Remove unbalanced and unneeded mutex unlock

The mutex unlock in the threaded interrupt handler is not paired
with any mutex lock. Remove it.

This bug has been here for a really long time, so it applies
to any stable repo.

Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>