ARM: PL08x: prevent dma_set_runtime_config() reconfiguring memcpy channels

Prevent dma_set_runtime_config() being used to alter the configuration
supplied by the platform for memcpy channel configuration.  No one
should be trying to change this configuration.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/dma/amba-pl08x.c

@@ -1129,6 +1129,9 @@ static int dma_set_runtime_config(struct dma_chan *chan,
 	u32 cctl = 0;
 	int i;
 
+	if (!plchan->slave)
+		return -EINVAL;
+
 	/* Transfer direction */
 	plchan->runtime_direction = config->direction;
 	if (config->direction == DMA_TO_DEVICE) {