mmc: meson-mx-sdhc: Fix error check for dma_map_sg

dma_map_sg return 0 on error, also change the type for dma_len
from int to unsigned int.

Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Kevin Hilman <khilman@baylibre.com>
Cc: Jerome Brunet <jbrunet@baylibre.com>
Cc: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Link: https://lore.kernel.org/r/20220825074008.33349-2-jinpu.wang@ionos.comSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/meson-mx-sdhc-mmc.c

@@ -381,14 +381,14 @@ static void meson_mx_sdhc_set_ios(struct mmc_host *mmc, struct mmc_ios *ios)
 static int meson_mx_sdhc_map_dma(struct mmc_host *mmc, struct mmc_request *mrq)
 {
 	struct mmc_data *data = mrq->data;
-	int dma_len;
+	unsigned int dma_len;
 
 	if (!data)
 		return 0;
 
 	dma_len = dma_map_sg(mmc_dev(mmc), data->sg, data->sg_len,
 			     mmc_get_dma_dir(data));
-	if (dma_len <= 0) {
+	if (!dma_len) {
 		dev_err(mmc_dev(mmc), "dma_map_sg failed\n");
 		return -ENOMEM;
 	}