scripts: sphinx-pre-install: fix venv version check logic

The logic which checks if the venv version is good enough
but was not activated is broken: it is checking against
the wrong val, making it to recommend to re-create a venv
every time. Fix it.

Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Link: https://lore.kernel.org/r/afe01b7863fd655986d84ace8948f3d7aede796d.1656756450.git.mchehab@kernel.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>