[media] coda: simplify optional reset handling

As of commit bb475230

 ("reset: make optional functions really
optional"), the reset framework API calls use NULL pointers to
describe optional, non-present reset controls.

This allows to return errors from devm_reset_control_get_optional
without special cases and to call reset_control_reset unconditionally.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>