net: dsa: qca8k: check correct variable in qca8k_phy_eth_command()

This is a copy and paste bug.  It was supposed to check "clear_skb"
instead of "write_skb".

Fixes: 2cd54856 ("net: dsa: qca8k: add support for phy read/write with mgmt Ethernet")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/qca8k.c

@@ -1018,7 +1018,7 @@ qca8k_phy_eth_command(struct qca8k_priv *priv, bool read, int phy,
 
 	clear_skb = qca8k_alloc_mdio_header(MDIO_WRITE, QCA8K_MDIO_MASTER_CTRL, &clear_val,
 					    QCA8K_ETHERNET_PHY_PRIORITY, sizeof(clear_val));
-	if (!write_skb) {
+	if (!clear_skb) {
 		ret = -ENOMEM;
 		goto err_clear_skb;
 	}