[mlir] Fix redundant return in the void method.

clang-tidy, fix redundant return statement at the end of the void method.

Reviewed By: jpienaar

Differential Revision: https://reviews.llvm.org/D111251

Author: rdzhabarov

mlir/lib/TableGen/Pattern.cpp

@@ -820,5 +820,4 @@ void Pattern::collectBoundSymbols(DagNode tree, SymbolInfoMap &infoMap,
                       "unsupported right now",
                       treeName));
   }
-  return;
 }