nir: fix compilation warning on glsl_get_internal_ifc_packing

Removes following warning:
   warning: 'const' type qualifier on return type has no effect

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4111>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4111>

src/compiler/nir_types.cpp

@@ -772,7 +772,7 @@ glsl_type_get_image_count(const struct glsl_type *type)
    return 0;
 }
 
-const enum glsl_interface_packing
+enum glsl_interface_packing
 glsl_get_internal_ifc_packing(const struct glsl_type *type,
                               bool std430_supported)
 {

src/compiler/nir_types.h

@@ -52,7 +52,7 @@ int glsl_get_struct_field_offset(const struct glsl_type *type,
 const struct glsl_struct_field *
 glsl_get_struct_field_data(const struct glsl_type *type, unsigned index);
 
-const enum glsl_interface_packing
+enum glsl_interface_packing
 glsl_get_internal_ifc_packing(const struct glsl_type *type,
                               bool std430_supported);