[mlir] Apply ClangTidyLegacy finding (NFC)

virtual is redundant since the function is already declared override.

Author: akuegel

mlir/include/mlir/Target/LLVM/NVVM/Utils.h

@@ -55,7 +55,7 @@ class SerializeGPUModuleBase : public LLVM::ModuleToObject {
   LogicalResult appendStandardLibs();
 
   /// Loads the bitcode files in `librariesToLink`.
-  virtual std::optional<SmallVector<std::unique_ptr<llvm::Module>>>
+  std::optional<SmallVector<std::unique_ptr<llvm::Module>>>
   loadBitcodeFiles(llvm::Module &module) override;
 
 protected: