realtek: fix ZyXEL initramfs image generation

The current rule produces empty trailers, causing the OEM firmware
update application to reject our images.

The double expansion of a makefile variable does not work inside
shell code.  The second round is interpreted as a shell expansion,
attempting to run the command ZYXEL_VERS instead of expanding the
$(ZYXEL_VERS) makefile variable.

Fix by removing one level of variable indirection.

Fixes: c6c8d597e183 ("realtek: Add generic zyxel_gs1900 image definition")
Tested-by: Sander Vanheule <[email protected]>
Signed-off-by: Bjørn Mork <[email protected]>

target/linux/realtek/image/Makefile

@@ -10,7 +10,7 @@ DEVICE_VARS += ZYXEL_VERS
 
 define Build/zyxel-vers
        ( echo VERS;\
-       for hw in $(1); do\
+       for hw in $(ZYXEL_VERS); do\
                echo -n "V9.99($$hw.0) | ";\
                date -d @$(SOURCE_DATE_EPOCH) +%m/%d/%Y;\
        done ) >> $@
@@ -117,7 +117,7 @@ define Device/zyxel_gs1900
   IMAGE_SIZE := 6976k
   DEVICE_VENDOR := ZyXEL
   UIMAGE_MAGIC := 0x83800000
-  KERNEL_INITRAMFS := kernel-bin | append-dtb | gzip | zyxel-vers $$$$(ZYXEL_VERS) | \
+  KERNEL_INITRAMFS := kernel-bin | append-dtb | gzip | zyxel-vers | \
 	uImage gzip
 endef