iso9660: fix build after af52661d (linux: rename LINUX26 to LINUX)

iso9660 used LINUX26_IMAGE_PATH, which got renamed. Adjust to match
the new name.

Reported-by: Sven Neumann <s.neumann@raumfeld.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

fs/iso9660/iso9660.mk

@@ -21,7 +21,7 @@ $(BINARIES_DIR)/rootfs.iso9660: host-cdrkit host-fakeroot linux26 rootfs-ext2 gr
 	mkdir -p $(ISO9660_TARGET_DIR)/boot/grub
 	cp $(GRUB_DIR)/stage2/stage2_eltorito $(ISO9660_TARGET_DIR)/boot/grub/
 	cp $(ISO9660_BOOT_MENU) $(ISO9660_TARGET_DIR)/boot/grub/menu.lst
-	cp $(LINUX26_IMAGE_PATH) $(ISO9660_TARGET_DIR)/kernel
+	cp $(LINUX_IMAGE_PATH) $(ISO9660_TARGET_DIR)/kernel
 	cp $(BINARIES_DIR)/rootfs.ext2 $(ISO9660_TARGET_DIR)/initrd
 	# Use fakeroot to pretend all target binaries are owned by root
 	rm -f $(FAKEROOT_SCRIPT)