fix nvidia line part count

Summary:
the format line above has 8 parts, on my system I also get 8 parts. since
we only access up to element 5 we only need to check >=5 though. the
actual line format is already validated above, so we can be fairly loose
with our requirements here.

Test Plan:
- have nvidia
- shows data with patch

Reviewers: davidedmundson, ahiemstra

Reviewed By: davidedmundson

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D24694