greybus: timesync: Do not hold mutex on cancel_delayed_work_sync
There is a scenario where gb_timesync_svc_remove() can run, attain a mutex
and call cancel_delayed_work_sync(). In the meantime a worker may already
be running and trying to attain the same mutex but will never do so as the
gb_timesync_svc_remove() path is holding the mutex and waiting on the
delayed_work_sync() to complete - leading to deadlock. This patch addresses
by calling the cancel_delayed_work_sync() before locking the relevant
mutex.