drm/mcde: Fix uninitialized value

"val" isn't initialized on the default: errorpath.
Just return from the function if this happens.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201119140707.1008407-1-linus.walleij@linaro.org