Bluetooth: Fix not checking for valid hdev on bt_dev_{info,warn,err,dbg}

This fixes attemting to print hdev->name directly which causes them to
print an error:

kernel: read_version:367: (efault): sock 000000006a3008f2
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

include/net/bluetooth/bluetooth.h

@@ -204,19 +204,21 @@ void bt_err_ratelimited(const char *fmt, ...);
 #define BT_DBG(fmt, ...)	pr_debug(fmt "\n", ##__VA_ARGS__)
 #endif
 
+#define bt_dev_name(hdev) ((hdev) ? (hdev)->name : "null")
+
 #define bt_dev_info(hdev, fmt, ...)				\
-	BT_INFO("%s: " fmt, (hdev)->name, ##__VA_ARGS__)
+	BT_INFO("%s: " fmt, bt_dev_name(hdev), ##__VA_ARGS__)
 #define bt_dev_warn(hdev, fmt, ...)				\
-	BT_WARN("%s: " fmt, (hdev)->name, ##__VA_ARGS__)
+	BT_WARN("%s: " fmt, bt_dev_name(hdev), ##__VA_ARGS__)
 #define bt_dev_err(hdev, fmt, ...)				\
-	BT_ERR("%s: " fmt, (hdev)->name, ##__VA_ARGS__)
+	BT_ERR("%s: " fmt, bt_dev_name(hdev), ##__VA_ARGS__)
 #define bt_dev_dbg(hdev, fmt, ...)				\
-	BT_DBG("%s: " fmt, (hdev)->name, ##__VA_ARGS__)
+	BT_DBG("%s: " fmt, bt_dev_name(hdev), ##__VA_ARGS__)
 
 #define bt_dev_warn_ratelimited(hdev, fmt, ...)			\
-	bt_warn_ratelimited("%s: " fmt, (hdev)->name, ##__VA_ARGS__)
+	bt_warn_ratelimited("%s: " fmt, bt_dev_name(hdev), ##__VA_ARGS__)
 #define bt_dev_err_ratelimited(hdev, fmt, ...)			\
-	bt_err_ratelimited("%s: " fmt, (hdev)->name, ##__VA_ARGS__)
+	bt_err_ratelimited("%s: " fmt, bt_dev_name(hdev), ##__VA_ARGS__)
 
 /* Connection and socket states */
 enum {