Fix S1121: Assignments should not be made from within sub-expressions' should ignore chained assignments

[fmallet]

For instance, an issue is raised here and should not be:
cPos = curLineStart = 0;

Why? Because this is a not-uncommon practice, and the intent is clear and should not confuse maintainers. Additionally, there's not a lot to be gained by updating it to:

i = 0;
j = 0;
{code}
and it would perhaps be a regression in terms of readability to update it to
{code}
i = 0;
j = i;

Relates to RSPEC-1121 Assignments should not be made from within sub-expressions