fix CUDAToolkit_LIBRARY_ROOT DEFINED check

Author: x12301450

mlir/lib/Target/LLVM/CMakeLists.txt

@@ -59,7 +59,7 @@ if ("NVPTX" IN_LIST LLVM_TARGETS_TO_BUILD)
     # See: https://gitlab.kitware.com/cmake/cmake/-/issues/24858
     # TODO: Bump the MLIR CMake version to 3.26.4 and switch to
     # ${CUDAToolkit_LIBRARY_ROOT}
-    if(NOT DEFINED ${CUDAToolkit_LIBRARY_ROOT})
+    if(NOT DEFINED CUDAToolkit_LIBRARY_ROOT)
       get_filename_component(MLIR_CUDAToolkit_ROOT ${CUDAToolkit_BIN_DIR}
                              DIRECTORY ABSOLUTE)
     else()