Otherwise, we are left with pretty bogus message saying that the pixel
format is not supported while leaving the details to the telepatic powers.

v2: use DRM_DEBUG_KMS instead of DRM_ERROR
Signed-off-by: NEugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>