Update the comments for ComputeMaskedBits, which lost its Mask parameter
in r154011.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208757 91177308-0d34-0410-b5e6-96231b3b80d8
Fix strange typo in markup.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208759 91177308-0d34-0410-b5e6-96231b3b80d8