drm/amdgpu: make sure we unpin the UVD BO

commit 07438603a07e52f1c6aa731842bd298d2725b7be upstream.

Releasing pinned BOs is illegal now. UVD 6 was missing from:
commit 2f40801dc553 ("drm/amdgpu: make sure we unpin the UVD BO")

Fixes: 2f40801dc553 ("drm/amdgpu: make sure we unpin the UVD BO")
Cc: stable@vger.kernel.org
Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>