[llvm-mca] Correctly set aliases for register writes introduced by optimized register...

[llvm-mca] Correctly set aliases for register writes introduced by optimized register moves.

This fixes a problem introduced by r344334. A write from a non-zero move
eliminated at register renaming stage was not correctly handled by the PRF. This
would have led to an assertion failure if the processor model declares a PRF
that enables non-zero move elimination.

llvm-svn: 344392