ieee802154: atusb: fix driver to work with older firmware versions

After the addition of the frame_retries callback we could run into cases where
a ATUSB device with an older firmware version would now longer be able to bring
the interface up.

We keep this functionality disabled now if the minimum firmware version for this
feature is not available.

Fixes: 5d82288b

 ("ieee802154: atusb: implement .set_frame_retries
ops callback")
Reported-by: Alexander Aring <aar@pengutronix.de>
Acked-by: Alexander Aring <aar@pengutronix.de>
Signed-off-by: Stefan Schmidt <stefan@osg.samsung.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>