nir: Properly invalidate metadata in nir_split_var_copies().
Signed-off-by:Kenneth Graunke <kenneth@whitecape.org> Reviewed-by:
Jason Ekstrand <jason.ekstrand@intel.com> Reviewed-by:
Eduardo Lima Mitev <elima@igalia.com> Cc: mesa-stable@lists.freedesktop.org (cherry picked from commit 8bb44510)