Fix the following warning:
panel-visionox-vtdr6130.c:249:12: warning: 'ret' is used uninitialized [-Wuninitialized]

Fixes: 9402cde9 ("drm/panel: vtdr6130: Use 16-bit brightness function")
Reported-by: Daniel Vetter <daniel@ffwll.ch>
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230119-topic-sm8550-vtdr6130-fixup-v1-1-82c4fb008138@linaro.org