clearfog: flashing: keep the watchdog happy

Without this, the process dies because the bootloader has already
preconfigured the WDT for us.

Change-Id: Ia1ac04bc80482d7ac1cc0743691d7780cd77deef
diff --git a/board/czechlight/clearfog/usb-reflash-factory.sh b/board/czechlight/clearfog/usb-reflash-factory.sh
index 6cde550..dac3a30 100644
--- a/board/czechlight/clearfog/usb-reflash-factory.sh
+++ b/board/czechlight/clearfog/usb-reflash-factory.sh
@@ -15,6 +15,8 @@
 # yellow blinking
 i2cset -y 1 0x60 0x16 0x0f || true
 
+watchdog /dev/watchdog
+
 mkdir /tmp/sdcard.image
 mount /mnt/sdcard.img.squashfs /tmp/sdcard.image/
 blkdiscard /dev/mmcblk0