[llvm] [TableGen] Use MVT instead of MVT::SimpleValueType. NFC (PR #169180)

[Sergei Barannikov via llvm-commits]

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@@ -556,17 +556,17 @@ static void FactorScope(std::unique_ptr<Matcher> &MatcherPtr) {
   // If all the options are CheckType's, we can form the SwitchType, woot.
   if (AllTypeChecks) {
     DenseMap<unsigned, unsigned> TypeEntry;
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s-barannikov wrote:

Can MVT be used as the key?

https://github.com/llvm/llvm-project/pull/169180