media: mt9m111: Fix error handling in mt9m111_power_on

The mt9m111_power_on function did not properly clean up whenever it
encountered an error. Do that now.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>