spi-mxs: Fix chipselect glitch

There was a change in the mxs-dma engine that uses a new custom flag.
The change was not applied to the mxs spi driver.
This results in chipselect being deasserted too early.
This fixes the chipselect problem by using the new flag in the mxs-spi
driver.

Fixes: ceeeb99c ("dmaengine: mxs: rename custom flag")
Signed-off-by: Ralf Schlatterbeck <rsc@runtux.com>
Link: https://msgid.link/r/20240202115330.wxkbfmvd76sy3a6a@runtux.com


Signed-off-by: Mark Brown <broonie@kernel.org>