staging: wfx: Make function 'wfx_tx_queue_get' static

Fix sparse warnings:

drivers/staging/wfx/queue.c:218:16: warning: symbol 'wfx_tx_queue_get' was not declared. Should it be static?
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Reviewed-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/1570629030-29888-3-git-send-email-zhengbin13@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wfx/queue.c

@@ -215,7 +215,9 @@ void wfx_tx_queue_put(struct wfx_dev *wdev, struct wfx_queue *queue, struct sk_b
 	spin_unlock_bh(&queue->queue.lock);
 }
 
-struct sk_buff *wfx_tx_queue_get(struct wfx_dev *wdev, struct wfx_queue *queue, u32 link_id_map)
+static struct sk_buff *wfx_tx_queue_get(struct wfx_dev *wdev,
+					struct wfx_queue *queue,
+					u32 link_id_map)
 {
 	struct sk_buff *skb = NULL;
 	struct sk_buff *item;