Fix copy+paste typo in doxygen parameter name to fix Wdocumentation. NFCI.

Author: RKSimon

llvm/include/llvm/Analysis/IRSimilarityIdentifier.h

@@ -462,7 +462,7 @@ class IRSimilarityCandidate {
 
 public:
   /// \param StartIdx - The starting location of the region.
-  /// \param StartIdx - The length of the region.
+  /// \param Len - The length of the region.
   /// \param FirstInstIt - The starting IRInstructionData of the region.
   /// \param LastInstIt - The ending IRInstructionData of the region.
   IRSimilarityCandidate(unsigned StartIdx, unsigned Len,