We recently added locking to add_queue_mes() but this error path was
overlooked.  Add an unlock to the error path.

Fixes: 1802b042 ("drm/amdgpu/kfd: remove is_hws_hang and is_resetting")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>