drm/amdgpu: Fix memory trashing if UVD ring test fails

fence_put was called on an uninitialized variable.
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Jay Cornwall <jay@jcornwall.me>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_uvd.c

@@ -1187,7 +1187,8 @@ int amdgpu_uvd_ring_test_ib(struct amdgpu_ring *ring, long timeout)
 		r = 0;
 	}
 
-error:
 	fence_put(fence);
+
+error:
 	return r;
 }