mmc: sdhci: Clear unused bounce buffer at DMA mmap error path

When DMA-mapping of the bounce buffer fails, the driver tries to fall
back, but it leaves the allocated host->bounce_buffer although its
size is zero.  Later on, the driver checks the use of bounce buffer
with host->bounce_buffer pointer, and it tries to use the buffer
incorrectly, resulting in Oops.

This patch clears the release the unused buffer and clears the
bounce_buffer pointer for addressing the problem.
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20210611101948.18972-1-tiwai@suse.deSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/sdhci.c

@@ -4072,9 +4072,13 @@ static void sdhci_allocate_bounce_buffer(struct sdhci_host *host)
 					   bounce_size,
 					   DMA_BIDIRECTIONAL);
 	ret = dma_mapping_error(mmc_dev(mmc), host->bounce_addr);
-	if (ret)
+	if (ret) {
+		devm_kfree(mmc_dev(mmc), host->bounce_buffer);
+		host->bounce_buffer = NULL;
 		/* Again fall back to max_segs == 1 */
 		return;
+	}
+
 	host->bounce_buffer_size = bounce_size;
 
 	/* Lie about this since we're bouncing */