drivers: net: ldpaa_eth: lx2160a: fix bug in checking if a DPMAC is enabled

The next DPMAC was always verified if it is enabled.  In case of
DPMAC@6, the DPMAC@7 is verified.  As DPMAC@7 is disabled, DPMAC@6 will
be considered disabled and not detected by uboot.
Signed-off-by: Grigore Popescu <grigore.popescu@nxp.com>
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>

drivers/net/ldpaa_eth/lx2160a.c

 // SPDX-License-Identifier: GPL-2.0+
 /*
- * Copyright 2018 NXP
+ * Copyright 2018, 2020 NXP
  */
 #include <common.h>
 #include <phy.h>
@@ -57,7 +57,7 @@ phy_interface_t wriop_dpmac_enet_if(int dpmac_id, int lane_prtcl)
 {
 	enum srds_prtcl;
 
-	if (is_device_disabled(dpmac_id + 1))
+	if (is_device_disabled(dpmac_id))
 		return PHY_INTERFACE_MODE_NONE;
 
 	if (lane_prtcl >= SGMII1 && lane_prtcl <= SGMII18)