net/core/dev.c: fix kernel-doc warning

Fix kernel-doc warning:

Warning(net/core/dev.c:5745): No description found for parameter 'dev'
Signed-off-by: NRandy Dunlap <rdunlap@xenotime.net>
Cc:	"David S. Miller" <davem@davemloft.net>
Cc:	netdev@vger.kernel.org
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -5744,6 +5744,7 @@ EXPORT_SYMBOL(netdev_refcnt_read);
 
 /**
  * netdev_wait_allrefs - wait until all references are gone.
+ * @dev: target net_device
  *
  * This is called when unregistering network devices.
  *