test/py: efi_secboot: fix additional pylint errors

This is a fixup by autopep8 after the commit ("test/py: efi_secboot:
apply autopep8").

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>