media: mt9m111: make SUBDEV_G_FMT ioctl work with SUBDEV_FORMAT_TRY

The VIDIOC_SUBDEV_G_FMT ioctl for this driver doesn't recognize
V4L2_SUBDEV_FORMAT_TRY and always works as if V4L2_SUBDEV_FORMAT_ACTIVE
is specified.

Cc: Enrico Scholz <enrico.scholz@sigma-chemnitz.de>
Cc: Michael Grzeschik <m.grzeschik@pengutronix.de>
Cc: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>