drm/vmwgfx: Use VMW_DEBUG_KMS for vmwgfx mode-setting user errors

For errors during layout change ioctl use VMW_DEBUG_KMS instead of
DRM_ERROR.

Signed-off-by: Deepak Rawat <drawat@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>