MD5_std.c should use HH2() also in its 2x interleaved code

[solardiz]

@magnumripper's commit a649032 introduced "common subexpressions in round 3" optimizations into many of our source files implementing (pieces of) MD4 and MD5. However, in MD5_std.c it did so only for the non-interleaved version of the code and missed the interleaved version. We could want to extend this optimization to that version as well.

This is our legacy scalar code, which rarely matters these days. But it does still have some uses.