at86rf230: remove tabs after define

This patch cleanups the at86rf230 driver to use a space instead a tab
after define.
Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Reviewed-by: Varka Bhadram <varkabhadram@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>