devlink: fix flexible_array.cocci warning

Fix following coccicheck warning:
./net/core/devlink.c:69:6-10: WARNING use flexible-array member instead

Signed-off-by: Guo Zhengkui <guozhengkui@vivo.com>
Link: https://lore.kernel.org/r/20211103121607.27490-1-guozhengkui@vivo.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/devlink.c

@@ -66,7 +66,7 @@ struct devlink {
 	u8 reload_failed:1;
 	refcount_t refcount;
 	struct completion comp;
-	char priv[0] __aligned(NETDEV_ALIGN);
+	char priv[] __aligned(NETDEV_ALIGN);
 };
 
 void *devlink_priv(struct devlink *devlink)