This PR fixes a minor bug in the `add_offload_test_device_code` CMake
helper function in `offload/unittests/CMakeLists.txt`.
The function was discovering the local CUDA Toolkit path and storing it
in the `cuda_path` variable but was then using the incorrect `CUDA_ROOT`
variable in the `add_custom_command` call for the NVPTX target.
This change corrects the command to use the intended `cuda_path`
variable.
acdc01b039