Fix memory leak upon failure of esp_vfs_fat_sdmmc_mount()

Closes https://github.com/espressif/esp-idf/issues/4165

components/fatfs/src/vfs_fat_sdmmc.c

@@ -158,6 +158,8 @@ fail:
     ff_diskio_unregister(pdrv);
     free(s_card);
     s_card = NULL;
+    free(s_base_path);
+    s_base_path = NULL;
     return err;
 }