spirv: Fix glsl type assert in spir2nir.

Fixes: 624789e3 "compiler/glsl: handle case where we have multiple users for types"
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
(cherry picked from commit 96c9483c)

Conflicts:
	src/compiler/spirv/spirv2nir.c