mrf24j40: remove spi settings overwrite

This patch removes spi settings while mrf24j40 probing. These settings
cannot be overwrite while device probing where spi controller should be
already configured. These settings need to be setup by device tree or
platform data.

Reviewed-by: Stefan Schmidt <stefan@osg.samsung.com>
Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>