[X86] Simplify some code in getInsertVINSERTImmediate and getExtractVEXTRACTImmediate. NFC

Replace one of the divides with a multiply.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@315162 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed