Bluetooth: hci_sync: Use cmd->num_cis instead of magic number

At the moment of the check, `cmd->num_cis` holds the value of 0x1f,
which is the max number of elements in the `cmd->cis[]` array at
declaration, which is 0x1f.

So, avoid using 0x1f directly, and instead use `cmd->num_cis`. Similarly
to this other patch[1].

Link: https://lore.kernel.org/linux-hardening/ZivaHUQyDDK9fXEk@neat/ [1]
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

net/bluetooth/hci_sync.c

@@ -6556,7 +6556,7 @@ int hci_le_create_cis_sync(struct hci_dev *hdev)
 		cis->cis_handle = cpu_to_le16(conn->handle);
 		aux_num_cis++;
 
-		if (aux_num_cis >= 0x1f)
+		if (aux_num_cis >= cmd->num_cis)
 			break;
 	}
 	cmd->num_cis = aux_num_cis;