media: i2c: mt9p031: Switch from OF to fwnode API

Remove the direct dependency on OF by using the fwnode API. This makes
the driver usable on non-OF systems, such as ACPI-based platforms.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>