wined3d: Ignore the blitter's depth/colour fill return value in wined3d_device_clear_rendertarget_view().

Direct3D 10 and later don't have a return value, earlier versions seem to
claim success even if the fill/clear is unsupported.
Signed-off-by: Henri Verbeet <hverbeet@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>