staging: wilc1000: fix variable signedness

txq_count receives a value from wilc_wlan_handle_txq()
and therefore should be u32

found using sparse:
drivers/staging/wilc1000/linux_wlan.c:306:58: warning:
 incorrect type in argument 2 (different signedness)
Signed-off-by: Ilia Sergachev <ilia.sergachev@unibas.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wilc1000/linux_wlan.c

@@ -283,7 +283,8 @@ int wilc_wlan_get_num_conn_ifcs(struct wilc *wilc)
 
 static int linux_wlan_txq_task(void *vp)
 {
-	int ret, txq_count;
+	int ret;
+	u32 txq_count;
 	struct wilc_vif *vif;
 	struct wilc *wl;
 	struct net_device *dev = vp;