[TW#17011] esp_vfs_fat_sdmmc_mount(): double call to free() is possible

[jkearins]

If f_mount() failes we will goto fail and in this case free(workbuf) will be called twice. We should reset workbuf pointer with workbuf=NULL after first call.

...
        free(workbuf); // first call
        workbuf = NULL; // <-- missed
        ESP_LOGW(TAG, "mounting again");
        res = f_mount(fs, drv, 0);
        if (res != FR_OK) {
            err = ESP_FAIL;
            ESP_LOGD(TAG, "f_mount failed after formatting (%d)", res);
            goto fail;
        }
    }
    return ESP_OK;

fail:
    sdmmc_host_deinit();
    free(workbuf); // second call
    if (fs) {
        f_mount(NULL, drv, 0);
    }
...