uboot-zynq: build with zynq generic subtarget

Fix image build fail by using the generic subtarget.

Fixes: 6d7129ef ("zynq: 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-zynq/Makefile

@@ -18,6 +18,7 @@ include $(INCLUDE_DIR)/host-build.mk
 
 define U-Boot/Default
   BUILD_TARGET:=zynq
+  BUILD_SUBTARGET:=generic
   UBOOT_IMAGE:=spl/boot.bin u-boot.img
   UBOOT_CONFIG:=zynq_$(1)
   UENV:=default