i965: Drop unused return value from intel_finalize_mipmap_tree().

i965: Drop unused return value from intel_finalize_mipmap_tree().

The old return type of GLuint was wonky - it should have been bool.
But nothing actually uses the return value anyway, so we can just drop
that and make it a void function.

In theory, it might make sense to ask whether the texture validated
successfully, but just checking intel_obj->mt != NULL works for that.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>