apm821xx: MBL: correct phy-mode delay settings

This came up in an upstream commit: "
b1dd9bf688b0 "net: phy: broadcom: Fix RGMII delays for BCM50160 and BCM50610M"

The PHY driver entry for BCM50160 and BCM50610M calls
bcm54xx_config_init() but does not call bcm54xx_config_clock_delay() in
order to configuration appropriate clock delays on the PHY, fix that."

So the "rgmii" phy-mode has always been wrong, but went unnoticed since
the broadcom phy driver didn't push the delay settings to the chip.

Signed-off-by: Christian Lamparter <chunkeey@gmail.com>

target/linux/apm821xx/dts/wd-mybooklive.dts

@@ -149,6 +149,7 @@
 	phy-map = <0x2>;
 	phy-address = <0x1>;
 	phy-handle = <&phy>;
+	phy-mode = "rgmii-id";
 
 	mdio {
 		#address-cells = <1>;