media: ov5640: Disable transparent feature for test pattern

The transparent feature for test patterns blends the test pattern with
an actual captured image. This makes the result non-static, subject to
changes in the sensor's field of view.

Test patterns should be predictable and deterministic, even if they are
dynamic patterns. Disable the transparent feature of the test pattern.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>