mmc: wbsd: safer check if dma_addr is valid DMA address

host->dma_addr can store a value that is not returned by the DMA API,
so it is safer to check if is a valid DMA address indirectly.
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/wbsd.c

@@ -1437,11 +1437,14 @@ static void wbsd_request_dma(struct wbsd_host *host, int dma)
 
 static void wbsd_release_dma(struct wbsd_host *host)
 {
-	if (!dma_mapping_error(mmc_dev(host->mmc), host->dma_addr)) {
+	/*
+	 * host->dma_addr is valid here iff host->dma_buffer is not NULL.
+	 */
+	if (host->dma_buffer) {
 		dma_unmap_single(mmc_dev(host->mmc), host->dma_addr,
 			WBSD_DMA_SIZE, DMA_BIDIRECTIONAL);
-	}
 		kfree(host->dma_buffer);
+	}
 	if (host->dma >= 0)
 		free_dma(host->dma);