dpaa2-mac: Fix potential null pointer dereference

There is a null-check for _pcs_, but it is being dereferenced
prior to this null-check. So, if _pcs_ can actually be null,
then there is a potential null pointer dereference that should
be fixed by null-checking _pcs_ before being dereferenced.

Addresses-Coverity-ID: 1497159 ("Dereference before null check")
Fixes: 94ae899b ("dpaa2-mac: add PCS support through the Lynx module")
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/dpaa2/dpaa2-mac.c

@@ -290,9 +290,9 @@ static int dpaa2_pcs_create(struct dpaa2_mac *mac,
 static void dpaa2_pcs_destroy(struct dpaa2_mac *mac)
 {
 	struct lynx_pcs *pcs = mac->pcs;
-	struct device *dev = &pcs->mdio->dev;
 
 	if (pcs) {
+		struct device *dev = &pcs->mdio->dev;
 		lynx_pcs_destroy(pcs);
 		put_device(dev);
 		mac->pcs = NULL;