fix(msc_test): fopen Werror=use-after-free

[peter-marcisovsky]

Description

Fixing build error of msc test app to unblock CI

Error error

/__w/esp-usb/esp-usb/host/class/msc/usb_host_msc/test_app/main/test_msc.c: In function 'write_read_file':
/__w/esp-usb/esp-usb/host/class/msc/usb_host_msc/test_app/main/test_msc.c:165:5: error: pointer 'f' may be used after 'fclose' [-Werror=use-after-free]
  165 |     fclose(f);
      |     ^~~~~~~~~
/__w/esp-usb/esp-usb/host/class/msc/usb_host_msc/test_app/main/test_msc.c:160:5: note: call to 'fclose' here
  160 |     fclose(f);
      |     ^~~~~~~~~
/__w/esp-usb/esp-usb/host/class/msc/usb_host_msc/test_app/main/test_msc.c:164:5: error: pointer 'f' may be used after 'fclose' [-Werror=use-after-free]
  164 |     fgets(line, sizeof(line), f);
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/__w/esp-usb/esp-usb/host/class/msc/usb_host_msc/test_app/main/test_msc.c:160:5: note: call to 'fclose' here
  160 |     fclose(f);
      |     ^~~~~~~~~
cc1: all warnings being treated as errors
[712/719] Building C object esp-idf/esp_tinyusb/CMakeFiles/__idf_esp_tinyusb.dir/tinyusb_msc.c.obj
ninja: build stopped: subcommand failed.
HINT: The warning(s) '-Werror=use-after-free' may appear after compiler update above [](https://jira.espressif.com:8443/browse/)

Related

Testing

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Checklist

Before submitting a Pull Request, please ensure the following:

• 🚨 This PR does not introduce breaking changes.
• All CI checks (GH Actions) pass.
• Documentation is updated as needed.
• Tests are updated or added as necessary.
• Code is well-commented, especially in complex areas.
• Git history is clean — commits are squashed to the minimum necessary.