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/include/dma-uclass.h b/include/dma-uclass.h
index a1d9d26..340437a 100644
--- a/include/dma-uclass.h
+++ b/include/dma-uclass.h
@@ -58,14 +58,14 @@
 	 */
 	int (*request)(struct dma *dma);
 	/**
-	 * free - Free a previously requested dma.
+	 * rfree - Free a previously requested dma.
 	 *
 	 * This is the implementation of the client dma_free() API.
 	 *
 	 * @dma: The DMA to free.
 	 * @return 0 if OK, or a negative error code.
 	 */
-	int (*free)(struct dma *dma);
+	int (*rfree)(struct dma *dma);
 	/**
 	 * enable() - Enable a DMA Channel.
 	 *