uboot-omap: build with omap generic subtarget

Fix image build fail by using the generic subtarget.

Fixes: b2bfea48 ("omap: add generic subtarget")
Ref: 40e3f660 ("uboot-fritz4040: build with ipq40xx generic subtarget")
Signed-off-by: Kuan-Yi Li <[email protected]>
[ add commit description ]
Signed-off-by: Christian Marangi <[email protected]>

package/boot/uboot-omap/Makefile

@@ -18,6 +18,7 @@ include $(INCLUDE_DIR)/package.mk
 
 define U-Boot/Default
   BUILD_TARGET:=omap
+  BUILD_SUBTARGET:=generic
   UBOOT_IMAGE:=u-boot.img MLO
 endef