executorch/examples/devtools/example_runner/example_runner.cpp: fix format mismatches printing error_code_t values (#6324)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/6324

This avoids the following errors:

  executorch/examples/devtools/example_runner/example_runner.cpp:224:7: error: format specifies type 'unsigned int' but the argument has type 'Error' [-Werror,-Wformat]
  executorch/examples/devtools/example_runner/example_runner.cpp:245:7: error: format specifies type 'unsigned int' but the argument has type 'Error' [-Werror,-Wformat]
  executorch/examples/devtools/example_runner/example_runner.cpp:255:7: error: format specifies type 'unsigned int' but the argument has type 'Error' [-Werror,-Wformat]
  executorch/examples/devtools/example_runner/example_runner.cpp:297:9: error: format specifies type 'unsigned int' but the argument has type 'Error' [-Werror,-Wformat]

Reviewed By: tarun292

Differential Revision: D64540817

fbshipit-source-id: 3f6154c801376bc10a1b7ff0f3e8994b47c8096a