Simplify code that tries to do vector extracts for shuffles when the mask width and...

Simplify code that tries to do vector extracts for shuffles when the mask width and the input vector widths don't match. No need to check the min and max are in range before calculating the start index. The range check after having the start index is sufficient. Also no need to check for an extract from the beginning differently.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154295 91177308-0d34-0410-b5e6-96231b3b80d8