glsl: fix subroutine uniform .length().

This fixes .length() on subroutine uniform arrays, if
we don't find the identifier normally, we look up the corresponding
subroutine identifier instead.

Fixes:
GL45-CTS.shader_subroutine.arrays_of_arrays_of_uniforms
GL45-CTS.shader_subroutine.arrayed_subroutine_uniforms

Reviewed-by: Chris Forbes <chrisforbes@google.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
1 file changed