mmc: jz4740_mmc: Fix error check for dma_map_sg

dma_map_sg return 0 on error.
Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Acked-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20220825074008.33349-3-jinpu.wang@ionos.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/jz4740_mmc.c

@@ -298,7 +298,7 @@ static int jz4740_mmc_prepare_dma_data(struct jz4740_mmc_host *host,
 {
 	struct dma_chan *chan = jz4740_mmc_get_dma_chan(host, data);
 	enum dma_data_direction dir = mmc_get_dma_dir(data);
-	int sg_count;
+	unsigned int sg_count;
 
 	if (data->host_cookie == COOKIE_PREMAPPED)
 		return data->sg_count;
@@ -308,7 +308,7 @@ static int jz4740_mmc_prepare_dma_data(struct jz4740_mmc_host *host,
 			data->sg_len,
 			dir);
 
-	if (sg_count <= 0) {
+	if (!sg_count) {
 		dev_err(mmc_dev(host->mmc),
 			"Failed to map scatterlist for DMA operation\n");
 		return -EINVAL;