spi: imx: fix ERR009165

Change to XCH  mode even in dma mode, please refer to the below
errata:
https://www.nxp.com/docs/en/errata/IMX6DQCE.pdf



Signed-off-by: Robin Gong <yibin.gong@nxp.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>