ramips: remove duplicate dts nodes of MediaTek LinkIt Smart 7688

There are two identical wmac nodes in the dts file of MediaTek
LinkIt Smart 7688, so delete one of them.
Signed-off-by: Jack Chen <redchenjs@live.com>
(cherry picked from commit 4be271a4)

target/linux/ramips/dts/LINKIT7688.dts

@@ -85,10 +85,6 @@
 	};
 };
 
-&wmac {
-	status = "okay";
-};
-
 &spi0 {
 	status = "okay";