format-code: ignore subprojects for pycodestyle

Meson-based repositories may have code from elsewhere inside
a 'subprojects' subdirectory, especially on a developer system.
Tell `pycodestyle` to ignore this subdirectory so there are not
false positive code format failures due to upstream code
repositories we do not have control over.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ia6ce4ba355b14aae07b7e346afaac8667399cfc1
1 file changed