[InstCombine] Use APInt::getBitsSetFrom to shortern a line and fix an 80 columns violation. NFC

Fix a similar line in the same function.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@331947 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed