media: staging: rkisp1: cap: remove support of BGR666 format

The rkisp1 supports RGB encoding with 6 bits per
color with the following format:
- - b5 b4 b3 b2 b1 b0 - - g5 g4 g3 g2 g1 g0 - - r5 r4 r3 r2 r1 r0 - - - - - - - -

This is not how V4L2_PIX_FMT_BGR666 is defined, so remove
this format from the driver's formats list.

Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
Acked-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>