net: broadcom: bcm4908_enet: fix RX path possible mem leak

After filling RX ring slot with new skb it's required to free old skb.
Immediately on error or later in the net subsystem.

Fixes: 4feffead ("net: broadcom: bcm4908enet: add BCM4908 controller driver")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20210224151842.2419-1-zajec5@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/broadcom/bcm4908_enet.c

@@ -570,6 +570,7 @@ static int bcm4908_enet_poll(struct napi_struct *napi, int weight)
 
 		if (len < ETH_ZLEN ||
 		    (ctl & (DMA_CTL_STATUS_SOP | DMA_CTL_STATUS_EOP)) != (DMA_CTL_STATUS_SOP | DMA_CTL_STATUS_EOP)) {
+			kfree_skb(slot.skb);
 			enet->netdev->stats.rx_dropped++;
 			break;
 		}