function_hooks: hack around fallout from moving the assignment to the end

function_hooks: hack around fallout from moving the assignment to the end

I moved the fake assignment to the end so that we would have already parsed
the PARAM_LIMIT before we do the assignment.  But then we run into stuff
like this:

int frob(struct whatever *p)
{
	int ret = p->a;

	kfree(p);
	return a;
}

So now we parse PARAM_FREE p and then fake an assignment "x = p->a;".  So
now we get errors that we're dereferencing "p" when it's freed.  My
solution is just to not generate those warnings when we're in a fake
assignment.  But then smatch_comparison starts ignoring those assignments
as well so we have to make it not ignore certain fake assignments...

It's a bit hacky, but I think it should work.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>