backends/drm: fix format sorting
As the drm format number of 10 bit colors is lower, the fallback sorting preferred those formats, even if KWIN_DRM_PREFER_COLOR_DEPTH=24 was set. To fix that, prefer 8 bit colors over something random.
As the drm format number of 10 bit colors is lower, the fallback sorting preferred those formats, even if KWIN_DRM_PREFER_COLOR_DEPTH=24 was set. To fix that, prefer 8 bit colors over something random.