tests: fs: Ensure file_path includes max file name length
tests: fs: Ensure file_path includes max file name length

A hardcoded path lenth of 80 will not be able to suppor the full length
of 255 when LFN is enabled. This does produce a compiler error,
thankfully, this is only applicable to the test cases.

Signed-off-by: Roman Vaughan <1620c2a00a7840d4515361aacd4b41348f2a8a7d@gmail.com>

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