drm/amdgpu:fix uvd ring fini routine(v2)

fix missing finish uvd enc_ring.
v2:
since the adev pointer check in already in ring_fini
so drop the check outsider

Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>