When dragging a Sash with the SWT.SMOOTH, the width and height of the
sash are erroneously scaled up by the current zoom. It is caused by a
recent change which replaced a setBoundsInPixels with a setBounds call
still using the same pixel-based width and height values.

This change adapts the according call to consistently use pixel-based
values passed to the setBoundsInPixels method again.

Fixes https://github.com/eclipse-platform/eclipse.platform.swt/issues/2329