util: fix MAKE_RGBA macro for 10bpp modes

We need to shift the values up, otherwise we'd end up with a negative
shift. This works for up-to 16-bit components, which is fine for now.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>