glsl: return failure from remove_unused_io_vars

to stop linking if we fail here.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34307>
1 file changed