media: nxp: imx8-isi: Factor out a variable

gcc-11 seems to believe that the coeffs variable can be used
uninitialized. Refactor the code and remove the cscen variable to
convince gcc that we are doing a good job.

drivers/media/platform/nxp/imx8-isi/imx8-isi-hw.c:218:20: warning: 'coeffs' may be used uninitialized in this function [-Wmaybe-uninitialized]

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/20240128-gcc-11-warnings-v1-1-52bbdf492049@chromium.org


Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>