copy-firmware.sh: call ./check_whence.py before parsing the file

copy-firmware.sh: call ./check_whence.py before parsing the file

Currently ./check_whence.py is used when submitting new firmware, while
copy-firmware.sh when the firmware is to be consumed.

Since the latter does (very little) validation, having a malformed WHENCE file
can lead to all sorted of problems. From the obvious, where it errors out, to
more serious one where it overwrites or executes something it should not have.

Just call check_whence.py and error out. It takes 0.2s on my 5 year old
mid-range laptop, so the overhead is negligible.

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>