net: caif: Add lockdep expression to RCU traversal primitive

caifdevs->list is traversed using list_for_each_entry_rcu()
outside an RCU read-side critical section but under the
protection of rtnl_mutex. Hence, add the corresponding lockdep
expression to silence the following false-positive warning:

[   10.868467] =============================
[   10.869082] WARNING: suspicious RCU usage
[   10.869817] 5.6.0-rc1-00177-g06ec0a154aae4 #1 Not tainted
[   10.870804] -----------------------------
[   10.871557] net/caif/caif_dev.c:115 RCU-list traversed in non-reader section!!

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Amol Grover <frextrite@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>