[RS6000] Correct constraints for ior<mode>_mask

ior<mode>_mask always splits to rtl matching rotl<mode>3_insert.  The
latter requires one of its input operands match the output, so let
reload/lra know the equivalent operand match must also occur for
ior<mode>_mask.

	PR target/67356
	* config/rs6000/rs6000.md (ior<mode>_mask): Use constraint "0"
	for operand 1.

From-SVN: r227260