spi: rockchip: disable spi on error

Successful transfers leave the spi disabled, so if
we just make sure to disable the spi on error
there should be no need to disable the spi from
master->unprepare_message.

This also flushes the tx and rx fifos,
so no need to do that manually.

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