net: phy: cortina: use get_nand_dev_by_index()

As part of preparation for nand DM conversion the new API has been
introduced to remove direct access to nand_info array. So, use it here
instead of accessing to nand_info array directly

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>

drivers/net/phy/cortina.c

@@ -139,7 +139,8 @@ void cs4340_upload_firmware(struct phy_device *phydev)
 	size_t fw_length = CONFIG_CORTINA_FW_LENGTH;
 
 	addr = malloc(CONFIG_CORTINA_FW_LENGTH);
-	ret = nand_read(nand_info[0], (loff_t)CONFIG_CORTINA_FW_ADDR,
+	ret = nand_read(get_nand_dev_by_index(0),
+			(loff_t)CONFIG_CORTINA_FW_ADDR,
 			&fw_length, (u_char *)addr);
 	if (ret == -EUCLEAN) {
 		printf("NAND read of Cortina firmware at 0x%x failed %d\n",