Bluetooth: hci_uart: add missing NULL check in h5_enqueue

Syzbot hit general protection fault in __pm_runtime_resume(). The problem
was in missing NULL check.

hu->serdev can be NULL and we should not blindly pass &serdev->dev
somewhere, since it will cause GPF.

Reported-by: syzbot+b9bd12fbed3485a3e51f@syzkaller.appspotmail.com
Fixes: d9dd833c ("Bluetooth: hci_h5: Add runtime suspend")
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/bluetooth/hci_h5.c

@@ -629,9 +629,11 @@ static int h5_enqueue(struct hci_uart *hu, struct sk_buff *skb)
 		break;
 	}
 
-	pm_runtime_get_sync(&hu->serdev->dev);
-	pm_runtime_mark_last_busy(&hu->serdev->dev);
-	pm_runtime_put_autosuspend(&hu->serdev->dev);
+	if (hu->serdev) {
+		pm_runtime_get_sync(&hu->serdev->dev);
+		pm_runtime_mark_last_busy(&hu->serdev->dev);
+		pm_runtime_put_autosuspend(&hu->serdev->dev);
+	}
 
 	return 0;
 }