uboot-lantiq: package does not build inside the SDK

the packages failed to build inside the SDK due to missing ethernet
firmware files.

Signed-off-by: John Crispin <john@phrozen.org>

package/boot/uboot-lantiq/Makefile

@@ -355,7 +355,7 @@ define Package/uboot/template
 define Package/uboot-lantiq-$(1)
   SECTION:=boot
   CATEGORY:=Boot Loaders
-  DEPENDS:=$(3)
+  DEPENDS:=$(3) @!IN_SDK
   TITLE:=$(2)
   URL:=http://www.denx.de/wiki/U-Boot
   VARIANT:=$(1)