utils/check-package: fix flake8 warning

Fix flake 8 warning (introduced with commit [1]):

  utils/checkpackagelib/lib.py:56:1: E302 expected 2 blank lines, found 1

[1] https://git.buildroot.net/buildroot/commit/?id=8e352c32b0beded97a8a5c1e9edc9d618514ee7b



Reported-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>