support/testing/tests/fs/test_f2fs: fix flake8 warning

This commit fixes the following flake8 warnings:

support/testing/tests/fs/test_f2fs.py:6:1: E302 expected 2 blank lines, found 1
support/testing/tests/fs/test_f2fs.py:12:1: E302 expected 2 blank lines, found 1
support/testing/tests/fs/test_f2fs.py:38:23: E225 missing whitespace around operator

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>