[llvm] [NFC][MC][DecoderEmitter] Simplify loop to find the best filter (PR #156237)

[Sergei Barannikov via llvm-commits]

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@@ -1473,26 +1473,21 @@ FilterChooser::findBestFilter(ArrayRef<bitAttr_t> BitAttrs, bool AllowMixed,
 
   // We have finished with the filter processings.  Now it's time to choose
   // the best performing filter.
-  unsigned BestIndex = 0;
-  bool AllUseless = true;
+  std::unique_ptr<Filter> *BestFilter = nullptr;
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s-barannikov wrote:

Pointer to pointer is a bit confusing. Can this be an iterator?
Or maybe replace the loop with max_element?

https://github.com/llvm/llvm-project/pull/156237