brcmfmac: fix use of dev_kfree_skb() in irq context

The USB part of the brcmfmac did a dev_kfree_skb() that resulted
in a warning in net/core/skbuff.c:

Jul 11 04:53:33 lb-bun-10 kernel: [53282.667745] WARNING: at
net/core/skbuff.c:490 skb_release_head_state+0xcc/0xe0()

The brcmutil modules provides brcmu_pkt_buf_free_skb() which takes
the context into account. This patch makes use of this function
instead of dev_kfree_skb().
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/brcm80211/brcmfmac/usb.c

@@ -519,7 +519,7 @@ static void brcmf_usb_tx_complete(struct urb *urb)
 	else
 		devinfo->bus_pub.bus->dstats.tx_errors++;
 
-	dev_kfree_skb(req->skb);
+	brcmu_pkt_buf_free_skb(req->skb);
 	req->skb = NULL;
 	brcmf_usb_enq(devinfo, &devinfo->tx_freeq, req);
 
@@ -540,7 +540,7 @@ static void brcmf_usb_rx_complete(struct urb *urb)
 		devinfo->bus_pub.bus->dstats.rx_packets++;
 	} else {
 		devinfo->bus_pub.bus->dstats.rx_errors++;
-		dev_kfree_skb(skb);
+		brcmu_pkt_buf_free_skb(skb);
 		brcmf_usb_enq(devinfo, &devinfo->rx_freeq, req);
 		return;
 	}
@@ -556,7 +556,7 @@ static void brcmf_usb_rx_complete(struct urb *urb)
 			brcmf_usb_rx_refill(devinfo, req);
 		}
 	} else {
-		dev_kfree_skb(skb);
+		brcmu_pkt_buf_free_skb(skb);
 	}
 	return;
 
@@ -588,7 +588,7 @@ static void brcmf_usb_rx_refill(struct brcmf_usbdev_info *devinfo,
 	if (ret == 0) {
 		brcmf_usb_enq(devinfo, &devinfo->rx_postq, req);
 	} else {
-		dev_kfree_skb(req->skb);
+		brcmu_pkt_buf_free_skb(req->skb);
 		req->skb = NULL;
 		brcmf_usb_enq(devinfo, &devinfo->rx_freeq, req);
 	}