ieee802154: atusb: do not use the stack for address fetching to make it DMA able

From 4.9 we should really avoid using the stack here as this will not be DMA
able on various platforms. This changes a buffer that was introduced in the
4.10 merge window.

Fixes: 6cc33eba ("ieee802154: atusb: try to read permanent extended
address from device")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Stefan Schmidt <stefan@osg.samsung.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>