drm/amd/powerplay: fix memory leak in cz_hwmgr backend

vddc_dep_on_dal_pwrl is allocated and initialized in cz_hwmgr_backend_init
Thus free the memory in cz_hwmgr_backend_fini

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org