BlockFrequency: Bump up the entry frequency a bit.

This is a band-aid to fix the most severe regressions we're seeing from basing
spill decisions on block frequencies, until we have a better solution.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184835 91177308-0d34-0410-b5e6-96231b3b80d8