sandbox: video: Fix building without SDL

This is currently broken. If SDL is not installed, SANDBOX_SDL becomes
false and build errors are generated, e.g.:

   test/dm/video.c:424: undefined reference to `sandbox_sdl_set_bpp'

Fix it by making the function return an error in this case.

Signed-off-by: Simon Glass <sjg@chromium.org>
1 file changed