[X86][SSE] Fix -Wsign-compare problems introduced in r314658

The refactoring in
"[X86][SSE] Add createPackShuffleMask helper function. NFCI."
resulted in warning when compiling the code (seen in build bots).

This patch restores some types from int to unsigned to avoid
those warnings.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@314667 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed