ramips: tp-link: use a temporary file per image for OKLI images

The squashfs images of the TP-Link RE200 v1 and RE210 v1 differ between
builds; the uncompressed kernel of the RE200 one was 271 bytes larger,
from its device tree on:

  -00001040: 6d00 0080 00cb 1a9e 0000 0000 0000 006f
  +00001040: 6d00 0080 00da 1b9e 0000 0000 0000 006f

The RE210 device tree is exactly 271 bytes larger than the RE200 one, so
the RE200 image carried the kernel of the RE210.

tplink-v1-okli-image puts kernel and rootfs together in
$(IMAGE_ROOTFS).factory or .sysupgrade, a name shared by all devices with
the same rootfs. Both devices are built at the same time, so one can
overwrite the file of the other between cp, cat and mktplinkfw, and an
image can end up with the kernel and device tree of the other device.

Link: https://github.com/openwrt/openwrt/pull/25816
Signed-off-by: Paul Spooren <mail@aparcar.org>

target/linux/ramips/image/common-tp-link.mk

@@ -2,16 +2,16 @@ DEVICE_VARS += TPLINK_FLASHLAYOUT TPLINK_HWID TPLINK_HWREV TPLINK_HWREVADD
 DEVICE_VARS += TPLINK_HVERSION TPLINK_BOARD_ID TPLINK_HEADER_VERSION
 
 define Build/tplink-v1-okli-image
-	cp $(IMAGE_KERNEL) $(IMAGE_ROOTFS).$(word 2,$(1))
-	cat $(IMAGE_ROOTFS) >> $(IMAGE_ROOTFS).$(word 2,$(1))
+	cp $(IMAGE_KERNEL) $@.rootfs
+	cat $(IMAGE_ROOTFS) >> $@.rootfs
 	-$(STAGING_DIR_HOST)/bin/mktplinkfw \
 		-H $(TPLINK_HWID) -W $(TPLINK_HWREV) -F $(TPLINK_FLASHLAYOUT) \
 		-N "$(VERSION_DIST)" -V $(REVISION) -m $(TPLINK_HEADER_VERSION) \
 		-k "$(KDIR)/loader-$(word 1,$(1)).$(LOADER_TYPE)" -E $(KERNEL_LOADADDR) \
-		-r $(IMAGE_ROOTFS).$(word 2,$(1)) -o $@.new -j -X 0x40000 \
+		-r $@.rootfs -o $@.new -j -X 0x40000 \
 		-a $(call rootfs_align,$(FILESYSTEM)) $(wordlist 3,$(words $(1)),$(1)) \
 		$(if $(findstring sysupgrade,$(word 2,$(1))),-s) && mv $@.new $@ || rm -f $@
-	rm -f $(IMAGE_ROOTFS).$(word 2,$(1))
+	rm -f $@.rootfs
 endef
 
 define Build/uImage-tplink-c9