mailbox: hi3660: Use device-managed registration API

Get rid of some boilerplate driver removal code by using the newly added
device-managed registration API.

Tested-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
1 file changed