kstyle: Fix class name to fix indeterminate progress bars animations

The Breeze implementation is older than qqc2-desktop-style framework, and historically it used to use different base class. Times has changed, along with base classes; but Breeze code did not -- instead the problem was workarounded on a org.kde.desktop side first with a dummy Timer that called updateItem(), then through more sophisticated QtQuick Animations types (which delivered smoother results thanks to being bound to refresh rate of a screen).

While this patch fixes the problem, it seems like a better solution should be possible or more cleanup opportunities are available:

1. no other breeze animations invoke methods through QMetaObject system;
2. why and how an object would be something other than KQuickStyleItem?

(cherry picked from commit 8d88a824)

Note: this is an unholy dirty manual cherry-pick because of dark times predating mandatory clang-format.