gemini: replace date placeholder

Replace the data placerholder in ImageInfo-itian_sq201 in a reproducible
way.

The code for the replace was accidentality dropped in 5bac623895
("gemini: unify and fix ib-nas4220b and sq201 image creation")

Signed-off-by: Mathias Kresin <dev@kresin.me>

target/linux/gemini/image/Makefile

@@ -71,6 +71,8 @@ define Build/nas4220b-sq201-images
 	cp $(IMAGE_KERNEL) $@.tmp/zImage
 	cp ./ImageInfo-$(1) $@.tmp/ImageInfo
 
+	sed -i -e "s/DATESTR/`date +%Y%m%d $(if $(SOURCE_DATE_EPOCH),--date "@$(SOURCE_DATE_EPOCH)")`/g" $@.tmp/ImageInfo
+
 	(cd $@.tmp; tar --sort=name --owner=0 --group=0 --numeric-owner -czf $@ * \
 		$(if $(SOURCE_DATE_EPOCH),--mtime="@$(SOURCE_DATE_EPOCH)"))