6lowpan: revert: add missing spin_lock_init()

Revert the commit 768f7c7c to initialize
spinlock in the more preferable way and make it static to avoid sparse
warning.
Signed-off-by: NAlexander Smirnov <alex.bluesman.smirnov@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ieee802154/6lowpan.c

@@ -123,7 +123,7 @@ struct lowpan_fragment {
 
 static unsigned short fragment_tag;
 static LIST_HEAD(lowpan_fragments);
-spinlock_t flist_lock;
+static DEFINE_SPINLOCK(flist_lock);
 
 static inline struct
 lowpan_dev_info *lowpan_dev_info(const struct net_device *dev)
@@ -1186,8 +1186,6 @@ static int lowpan_newlink(struct net *src_net, struct net_device *dev,
 	list_add_tail(&entry->list, &lowpan_devices);
 	mutex_unlock(&lowpan_dev_info(dev)->dev_list_mtx);
 
-	spin_lock_init(&flist_lock);
-
 	register_netdevice(dev);
 
 	return 0;