Bluetooth: Fix Suspicious RCU usage warnings

Bluetooth: Fix Suspicious RCU usage warnings

The following functions in hci_core are always called with
hdev->lock held. No need to use list_for_each_entry_rcu(), therefore
change the usage of list_for_each_entry_rcu() in these functions
to list_for_each_entry().

hci_link_keys_clear()
hci_smp_ltks_clear()
hci_smp_irks_clear()
hci_blocked_keys_clear()

Warning encountered with CONFIG_PROVE_RCU_LIST:

[   72.213184] =============================
[   72.213188] WARNING: suspicious RCU usage
[   72.213192] 5.6.0-rc1+ #5 Not tainted
[   72.213195] -----------------------------
[   72.213198] net/bluetooth/hci_core.c:2288 RCU-list traversed in non-reader section!!

[   72.213676] =============================
[   72.213679] WARNING: suspicious RCU usage
[   72.213683] 5.6.0-rc1+ #5 Not tainted
[   72.213685] -----------------------------
[   72.213689] net/bluetooth/hci_core.c:2298 RCU-list traversed in non-reader section!!

[   72.214195] =============================
[   72.214198] WARNING: suspicious RCU usage
[   72.214201] 5.6.0-rc1+ #5 Not tainted
[   72.214204] -----------------------------
[   72.214208] net/bluetooth/hci_core.c:2308 RCU-list traversed in non-reader section!!

[  333.456972] =============================
[  333.456979] WARNING: suspicious RCU usage
[  333.457001] 5.6.0-rc1+ #5 Not tainted
[  333.457007] -----------------------------
[  333.457014] net/bluetooth/hci_core.c:2318 RCU-list traversed in non-reader section!!

Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>