media: ov2680: Don't take the lock for try_fmt calls

On ov2680_set_fmt() calls with format->which == V4L2_SUBDEV_FORMAT_TRY,
ov2680_set_fmt() does not talk to the sensor.

So in this case there is no need to lock the sensor->lock mutex or
to check that the sensor is streaming.

Fixes: 3ee47cad ("media: ov2680: Add Omnivision OV2680 sensor driver")
Acked-by: Rui Miguel Silva <rmfrfs@gmail.com>
Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>