video: zynqmp: Prevent use of uninitialised variables

video: zynqmp: Prevent use of uninitialised variables

The variables 'offset_matrix' and 'csc_matrix' will be used
uninitialised if video->is_rgb is false. Correct the logic so the
attempt to use uninitialised variables is not made. Also remove the use
of these variables as they seem to serve no useful purpose just being
aliases for arrays.

This issue was found by Smatch.

Signed-off-by: Andrew Goodbody <andrew.goodbody@linaro.org>
Link: https://lore.kernel.org/r/20251001-video_zynqmp-v1-1-34f1e59b9c34@linaro.org
Signed-off-by: Michal Simek <michal.simek@amd.com>