regcprop: Return early in maybe_mode_change for unorder modes [PR124649]

regcprop: Return early in maybe_mode_change for unorder modes [PR124649]

Like r16-727-g2ec5082dd24cef but the call to partial_subreg_p happens
in a later place, maybe_mode_change.
For this example we have VNx4QImode and DImode which are not ordered.

Bootstrapped and tested on aarch64-linux-gnu.

	PR rtl-optimization/124649

gcc/ChangeLog:

	* regcprop.cc (maybe_mode_change): Return early
	for unordered modes.

gcc/testsuite/ChangeLog:

	* gcc.dg/torture/pr124649-1.c: New test.

Signed-off-by: Andrew Pinski <andrew.pinski@oss.qualcomm.com>