clearfog: Create valid squashfs images for USB flashing

If the squashfs file gets reused from the last time, then the file gets
renamed automagically. That's not what we want.

Change-Id: Iaff83dc24306cc18e820f1e1b749be4c9e6768e8
diff --git a/board/czechlight/clearfog/usb-flash-genimage.sh b/board/czechlight/clearfog/usb-flash-genimage.sh
index 3ef30dd..dd07342 100755
--- a/board/czechlight/clearfog/usb-flash-genimage.sh
+++ b/board/czechlight/clearfog/usb-flash-genimage.sh
@@ -4,7 +4,7 @@
 
 install -m 0644 -D ${BR2_EXTERNAL_CZECHLIGHT_PATH}/board/czechlight/clearfog/usb-reflash-factory.sh ${BINARIES_DIR}/usb-reflash-factory.sh
 
-mksquashfs ${BINARIES_DIR}/sdcard.img ${BINARIES_DIR}/sdcard.img.squashfs -root-owned -comp gzip -progress
+mksquashfs ${BINARIES_DIR}/sdcard.img ${BINARIES_DIR}/sdcard.img.squashfs -root-owned -comp gzip -progress -noappend
 
 GENIMAGE_TMP="${BUILD_DIR}/genimage.tmp"
 rm -rf "${GENIMAGE_TMP}"