Bluetooth: mgmt: Replace zero-length array with flexible-array member

There is a regular need in the kernel to provide a way to declare having
a dynamically sized set of trailing elements in a structure. Kernel code
should always use "flexible array members" for these cases. The older
style of one-element or zero-length arrays should no longer be used.
Reference:
https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arraysReported-by: NZeal Robot <zealci@zte.com.cn>
Signed-off-by: NChangcheng Deng <deng.changcheng@zte.com.cn>
Signed-off-by: NLuiz Augusto von Dentz <luiz.von.dentz@intel.com>

include/net/bluetooth/mgmt.h

@@ -1112,7 +1112,7 @@ struct mgmt_ev_adv_monitor_device_found {
 	__s8   rssi;
 	__le32 flags;
 	__le16 eir_len;
-	__u8   eir[0];
+	__u8   eir[];
 } __packed;
 
 #define MGMT_EV_ADV_MONITOR_DEVICE_LOST		0x0030