Documentation: fix incorrect macro referencing in mscc-phy-vsc8531.txt

Modify LINK_1000_ACTIVITY and LINK_100_ACTIVITY to VSC8531_LINK_1000_ACTIVITY
and VSC8531_LINK_100_ACTIVITY respectively in the example of ethernet-phy node
according to include/dt-bindings/net/mscc-phy-vsc8531.h.
Signed-off-by: Baisheng Gao <gaobaisheng@bonc.com.cn>
Link: https://lore.kernel.org/r/1627488086-200263-1-git-send-email-gaobaisheng@bonc.com.cnSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/net/mscc-phy-vsc8531.txt

@@ -67,7 +67,7 @@ Example:
                 compatible = "ethernet-phy-id0007.0570";
                 vsc8531,vddmac		= <3300>;
                 vsc8531,edge-slowdown	= <7>;
-                vsc8531,led-0-mode	= <LINK_1000_ACTIVITY>;
-                vsc8531,led-1-mode	= <LINK_100_ACTIVITY>;
+                vsc8531,led-0-mode	= <VSC8531_LINK_1000_ACTIVITY>;
+                vsc8531,led-1-mode	= <VSC8531_LINK_100_ACTIVITY>;
 		load-save-gpios		= <&gpio 10 GPIO_ACTIVE_HIGH>;
         };