[media] s5p-fimc: Use correct fourcc for RGB565 colour format

With 16-bit RGB565 colour format pixels are stored by the device in memory
in the following order:

    | b3  | b2  | b1  | b0  |
   ~+-----+-----+-----+-----+
    | R5 G6 B5  | R5 G6 B5  |

This corresponds to V4L2_PIX_FMT_RGB565 fourcc, not V4L2_PIX_FMT_RGB565X.
This change is required to avoid trouble when setting up video pipeline
with the s5p-tv devices, so the colour formats at both devices can be
properly matched.

Cc: <stable@kernel.org>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>