dma: Rename free() to rfree()

This function name conflicts with our desire to #define free() to
something else on sandbox. Since it deals with resources, rename it to
rfree().

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/dma/dma-uclass.c b/drivers/dma/dma-uclass.c
index 5598bca..a0159d7 100644
--- a/drivers/dma/dma-uclass.c
+++ b/drivers/dma/dma-uclass.c
@@ -122,10 +122,10 @@
 
 	debug("%s(dma=%p)\n", __func__, dma);
 
-	if (!ops->free)
+	if (!ops->rfree)
 		return 0;
 
-	return ops->free(dma);
+	return ops->rfree(dma);
 }
 
 int dma_enable(struct dma *dma)