wifi: brcmutil: use helper function pktq_empty() instead of open code

pktq_empty was added in commit 5b435de0 ("net: wireless: add brcm80211
drivers") but it is currently not being utilized in some areas. This commit
replaces the open code with the pktq_empty() function.
Signed-off-by: Juhee Kang <claudiajkang@gmail.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230527114954.3281-2-claudiajkang@gmail.com

drivers/net/wireless/broadcom/brcm80211/brcmutil/utils.c

@@ -186,7 +186,7 @@ struct sk_buff *brcmu_pktq_peek_tail(struct pktq *pq, int *prec_out)
 {
 	int prec;
 
-	if (pq->len == 0)
+	if (pktq_empty(pq))
 		return NULL;
 
 	for (prec = 0; prec < pq->hi_prec; prec++)
@@ -223,7 +223,7 @@ struct sk_buff *brcmu_pktq_mdeq(struct pktq *pq, uint prec_bmp,
 	struct sk_buff *p;
 	int prec;
 
-	if (pq->len == 0)
+	if (pktq_empty(pq))
 		return NULL;
 
 	while ((prec = pq->hi_prec) > 0 &&