Revert "BlockFrequency: Saturate at 1 instead of 0 when multiplying a frequency with a branch probability."

This reverts commit r184584. Breaks PPC selfhost.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184590 91177308-0d34-0410-b5e6-96231b3b80d8