Adjust "end namespace" comment in MLIR to match new agree'd coding style

See D115115 and this mailing list discussion:
https://lists.llvm.org/pipermail/llvm-dev/2021-December/154199.html

Differential Revision: https://reviews.llvm.org/D115309

mlir/lib/Dialect/SparseTensor/Transforms/SparseTensorPasses.cpp

@@ -134,7 +134,7 @@ struct SparseTensorConversionPass
   }
 };
 
-} // end anonymous namespace
+} // namespace
 
 std::unique_ptr<Pass> mlir::createSparsificationPass() {
   return std::make_unique<SparsificationPass>();