Make host-specific tools available to rauc

...so that it can exec `mksquashfs`, for example.

Change-Id: I4548b2d069512aa5e0208bf5f81cfaa596e07f94
diff --git a/board/czechlight/clearfog/usb-flash-genimage.sh b/board/czechlight/clearfog/usb-flash-genimage.sh
index dd07342..c948bc0 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 ${BINARIES_DIR}/sdcard.img.squashfs -root-owned -comp gzip -progress -noappend
+${HOST_DIR}/bin/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}"