Linear Focus Algorithm 3.1, ignore timer-based focuser's return value.

Summary:
The return value seems unreliable, and, afterall probably doesn't represent reality.
Ths change causes the linear focus algorithm to assume that timer-based focusers
have moved the number of ms requested for their movement.

Test Plan:
There should be no changes to standard focus algorithms.
The only change would be with timer-based focusers (e.g. FCUSB) using the Linear Algorithm.
This didn't work previously (as I relied on the return value from the Indi, which is apparently unreliable).
That focuser should now autofocus with the linear focus algorithm, now changed to v3.1 in the menu.

Reviewers: mutlaqja

Reviewed By: mutlaqja

Subscribers: kde-edu

Tags: KDE Edu

Differential Revision: https://phabricator.kde.org/D26854