[PHITransAddr] Use std::find instead of std::count

There is no need to visit all the elements if we are merely performing a
membership check.  NFCI.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238701 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed