spirv: Drop a bogus assert

spirv: Drop a bogus assert

This was valid back when the only valid types of pointers were uint32
and uvec2.  Now that we're allowing more variety, it could be just about
anything so we'll just drop the assert.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Reviewed-by: Karol Herbst <kherbst@redhat.com>