ARM: dts: imx6qdl-sabreauto: Fix AR8031 phy-mode

As per kernel commit 0672d22a1924 ("ARM: dts: imx: Fix the AR803X phy-mode)
the correct phy-mode should be "rgmii-id", so fix it accordingly
to fix the Ethernet regression.

This problem has been exposed by commit:

commit 13114f38e2
Author: Vladimir Oltean <vladimir.oltean@nxp.com>
Date:   Thu May 7 00:11:51 2020 +0200

    phy: atheros: Explicitly disable RGMII delays

    To eliminate any doubts about the out-of-reset value of the PHY, that
    the driver previously relied on.

    If bisecting shows that this commit breaks your board you probably have
    a wrong PHY interface mode. You probably want the
    PHY_INTERFACE_MODE_RGMII_RXID or PHY_INTERFACE_MODE_RGMII_ID mode.

    Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
    Acked-by: Joe Hershberger <joe.hershberger@ni.com>

Fix the phy-mode accordingly to fix the regression.

Signed-off-by: Fabio Estevam <festevam@gmail.com>

arch/arm/dts/imx6qdl-sabreauto.dtsi

@@ -281,7 +281,7 @@
 &fec {
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_enet>;
-	phy-mode = "rgmii";
+	phy-mode = "rgmii-id";
 	interrupts-extended = <&gpio1 6 IRQ_TYPE_LEVEL_HIGH>,
 			      <&intc 0 119 IRQ_TYPE_LEVEL_HIGH>;
 	fsl,err006687-workaround-present;