[MCA] Slightly refactor method writeStartEvent in WriteState and ReadState. NFCI

This is another change in preparation for PR37494.
No functional change intended.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354261 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed