opengl: fix a typo in QOpenGLPaintDevice::dotsPerMeterY()

Fixes: QTBUG-95005

Pick-to: 6.2 6.1 5.15 5.12

Change-Id: I88ab9b757a5cfee520e07ac6280e31f9211342f0

Reviewed-by: Laszlo Agocs laszlo.agocs@qt.io

(cherry picked from commit 85831bcf)