spi: spi-fsl-dspi: Avoid NULL pointer in dspi_slave_abort for non-DMA mode

The driver does not create the dspi->dma structure unless operating in
DSPI_DMA_MODE, so it makes sense to check for that.

Fixes: f4b32390 ("spi: Introduce dspi_slave_abort() function for NXP's dspi SPI driver")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20200318001603.9650-8-olteanv@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-fsl-dspi.c

@@ -1192,8 +1192,10 @@ static int dspi_slave_abort(struct spi_master *master)
 	 * Terminate all pending DMA transactions for the SPI working
 	 * in SLAVE mode.
 	 */
-	dmaengine_terminate_sync(dspi->dma->chan_rx);
-	dmaengine_terminate_sync(dspi->dma->chan_tx);
+	if (dspi->devtype_data->trans_mode == DSPI_DMA_MODE) {
+		dmaengine_terminate_sync(dspi->dma->chan_rx);
+		dmaengine_terminate_sync(dspi->dma->chan_tx);
+	}
 
 	/* Clear the internal DSPI RX and TX FIFO buffers */
 	regmap_update_bits(dspi->regmap, SPI_MCR,