stm32f469-disco: replace $HOST_DIR/usr with $HOST_DIR in flash script
Manual change because the script uses ${OUTPUT_DIR}/host instead of
${HOST_DIR}.
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>