spi: rockchip: read transfer info directly

Just read transfer info directly from the spi device
and transfer structures rather than storing it in
driver data first.

Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Mark Brown <broonie@kernel.org>