dmaengine: imx-sdma: set sdmac->status to DMA_ERROR in err_out of sdma_prep_slave_sg()

sdma_prep_dma_cyclic() sets sdmac->status to DMA_ERROR in err_out,
and sdma_prep_slave_sg() needs to do the same.  Otherwise,
sdmac->status stays at DMA_IN_PROGRESS, which will make the function
return immediately next time it gets called.
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

drivers/dma/imx-sdma.c

@@ -947,6 +947,7 @@ static struct dma_async_tx_descriptor *sdma_prep_slave_sg(
 
 	return &sdmac->desc;
 err_out:
+	sdmac->status = DMA_ERROR;
 	return NULL;
 }