spi/omap2_mcspi: Check params before dereference or use

Check spi->chip_select for range before use.
Signed-off-by: Scott Ellis <scott@jumpnowtek.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/spi/omap2_mcspi.c

@@ -834,7 +834,6 @@ static void omap2_mcspi_cleanup(struct spi_device *spi)
 	struct omap2_mcspi_cs	*cs;
 
 	mcspi = spi_master_get_devdata(spi->master);
-	mcspi_dma = &mcspi->dma_channels[spi->chip_select];
 
 	if (spi->controller_state) {
 		/* Unlink controller state from context save list */
@@ -844,13 +843,17 @@ static void omap2_mcspi_cleanup(struct spi_device *spi)
 		kfree(spi->controller_state);
 	}
 
-	if (mcspi_dma->dma_rx_channel != -1) {
-		omap_free_dma(mcspi_dma->dma_rx_channel);
-		mcspi_dma->dma_rx_channel = -1;
-	}
-	if (mcspi_dma->dma_tx_channel != -1) {
-		omap_free_dma(mcspi_dma->dma_tx_channel);
-		mcspi_dma->dma_tx_channel = -1;
+	if (spi->chip_select < spi->master->num_chipselect) {
+		mcspi_dma = &mcspi->dma_channels[spi->chip_select];
+
+		if (mcspi_dma->dma_rx_channel != -1) {
+			omap_free_dma(mcspi_dma->dma_rx_channel);
+			mcspi_dma->dma_rx_channel = -1;
+		}
+		if (mcspi_dma->dma_tx_channel != -1) {
+			omap_free_dma(mcspi_dma->dma_tx_channel);
+			mcspi_dma->dma_tx_channel = -1;
+		}
 	}
 }