drm/i915: Error out when trying to set a y-tiled as a sprite

v2: Use a switch for consistency (Chris Wilson)

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>