FindCUDAToolkit: Fix search for sanitizer in cross-compilation

In a cross-compilation environment, `CUDAToolkit_LIBRARY_ROOT` will
be relative to the nvcc executable, rather than the cudart library,
due to `version.json` being relative to nvcc. However,
`CUDAToolkit_LIBRARY_SEARCH_DIRS` will be set correctly, so use
`EXTRA_PATH_SUFFIXES` to search relative to each entry in the list.