benchmark unaligned memory access

[YC Huang]

Thank you Nitsanw, running with "prof perfasm" shows there do have implicit Blackhole.consume():

....[Hottest Methods (after inlining)]..............................................................
 45.12%   23.97%  org.sample.MemoryAccessTest::alignedMemAccess
 29.23%   39.38%  org.sample.generated.MemoryAccessTest_alignedMemAccess::alignedMemAccess_avgt_jmhStub
 16.80%   30.44%  org.openjdk.jmh.infra.Blackhole::consume

I change the method to void Instead of return something, and assign the value to a class field,which seems could eliminate the implicit Blackhole.consume() and still avoid DCE...