spi/omap2_mcspi: fix NULL pointer dereference

Check spi->controller_state before dereferencing.

Shows up NULL here when using spi_alloc_device()/spi_add_device()
and spi_add_device() fails before spi_setup(). Calling spi_dev_put()
on the leftover spi_device results in the error.
Signed-off-by: Scott Ellis <scott@jumpnowtek.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/spi/omap2_mcspi.c

@@ -751,11 +751,13 @@ static void omap2_mcspi_cleanup(struct spi_device *spi)
 	mcspi = spi_master_get_devdata(spi->master);
 	mcspi_dma = &mcspi->dma_channels[spi->chip_select];
 
-	/* Unlink controller state from context save list */
-	cs = spi->controller_state;
-	list_del(&cs->node);
+	if (spi->controller_state) {
+		/* Unlink controller state from context save list */
+		cs = spi->controller_state;
+		list_del(&cs->node);
 
-	kfree(spi->controller_state);
+		kfree(spi->controller_state);
+	}
 
 	if (mcspi_dma->dma_rx_channel != -1) {
 		omap_free_dma(mcspi_dma->dma_rx_channel);