media: i2c: Switch exposure control unit to lines

The ov8865 driver currently has the unit of the V4L2_CID_EXPOSURE control
as 1/16th of a line. This is what the sensor expects, but isn't very
intuitive. Switch the control to be in units of a line and simply do the
16x multiplication before passing the value to the sensor.

The datasheet for this sensor gives minimum exposure as 2 lines, so take
the opportunity to correct the lower bounds of the control.

Signed-off-by: Daniel Scally <djrscally@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>