mmc: sandbox: Fix memory leak on probe failure

If mmc_init() fails, the buffer allocated by calloc() or mapped by
os_map_file() is not freed.

Free or unmap the buffer before returning the error.

Signed-off-by: Simon Glass <simon.glass@canonical.com>

drivers/mmc/sandbox_mmc.c

@@ -190,7 +190,16 @@ static int sandbox_mmc_probe(struct udevice *dev)
 		}
 	}
 
-	return mmc_init(&plat->mmc);
+	ret = mmc_init(&plat->mmc);
+	if (ret) {
+		if (plat->fname)
+			os_unmap(priv->buf, priv->size);
+		else
+			free(priv->buf);
+		return ret;
+	}
+
+	return 0;
 }
 
 static int sandbox_mmc_remove(struct udevice *dev)