staging: wlags49_h2: Fix sparse warning for static declaration

Fix the following sparse warning:
drivers/staging/wlags49_h2/wl_netdev.c:533:6: warning: symbol 'wl_poll'
was not declared. Should it be static?
Signed-off-by: Jelena Bjelja <jelena.bjelja.ing@gmail.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wlags49_h2/wl_netdev.c

@@ -530,7 +530,7 @@ int wl_ioctl( struct net_device *dev, struct ifreq *rq, int cmd )
 /*============================================================================*/
 
 #ifdef CONFIG_NET_POLL_CONTROLLER
-void wl_poll(struct net_device *dev)
+static void wl_poll(struct net_device *dev)
 {
     struct wl_private *lp = wl_priv(dev);
     unsigned long flags;