[TargetLowering] SimplifyDemandedBits - rename demanded mask args. NFCI.

Help stop bugs like rL343935 by making the 'original' DemandedBits arg more obviously not the mask that is actually used.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@344138 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed