spi: rockchip: simplify spi enable logic

Let the dma/non-dma code paths handle the spi enable
flag themselves. This removes some logic to determine
if the flag should be turned on before or after dma
and also don't leave the spi enabled if the dma path
fails.

Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
Signed-off-by: Mark Brown <broonie@kernel.org>