Improve Magnify and Ripple effects on video shader example

Re-enable Magnify shader.
Use correct coordinates for Magnify and Ripple shader.

Task-number: QTBUG-38121
Change-Id: Ie8d962ba841d074c9ebcf3b86f948848ad6a1812
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>