tests/amdgpu: Add return CUE_SUCCESS to suite_vcn_tests_clean.

    fixes: 806d0803 (amdgpu: Use new suite/test disabling functionality.)
    bug: https://bugs.freedesktop.org/show_bug.cgi?id=104280



Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>