at86rf230: copy pdata to driver allocated space

This patch copies the platform data in driver allocated space at first.
With this change we ensure that we access the allocated platform data as
readonly space.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Reported-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>