spi: mxs: Terminate DMA in case of DMA timeout

In case the SPI DMA times out, the DMA might still be in some kind of
inconsistent state. Issue dmaengine_terminate_all() on the particular
channel to kill off all operations before continuing.

Signed-off-by: Marek Vasut <marex@denx.de>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>