The "ret = " assignment was missing, so ov13b10_power_on() is not
checked for errors.  Add the assignment.

Fixes: 6e28afd1 ("media: ov13b10: add PM control support based on power resources")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Bingbu Cao <bingbu.cao@intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>