net/sched: taprio: taprio_dump and taprio_change are protected by rtnl_mutex

Since the writer-side lock is taken here, we do not need to open an RCU
read-side critical section, instead we can use rtnl_dereference() to
tell lockdep we are serialized with concurrent writes.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>