Add PySide compatibility function for QGLWidget.devicePixelRatioF

The call to this function added in change 2070063 broke usdview
when using PySide since this function was added in Qt 5.6. This
change patches in a simplified version of this function to
fix this.

(Internal change: 2070734)

pxr/usdImaging/usdviewq/qt.py

@@ -48,6 +48,9 @@ def GetPySideModule():
     if not hasattr(QtGui.QApplication, 'devicePixelRatio'):
         QtGui.QApplication.devicePixelRatio = lambda self: 1
 
+    if not hasattr(QtOpenGL.QGLWidget, 'devicePixelRatioF'):
+        QtOpenGL.QGLWidget.devicePixelRatioF = lambda self: 1.0
+
     if not hasattr(QtWidgets.QHeaderView, 'setSectionResizeMode'):
         QtWidgets.QHeaderView.setSectionResizeMode = \
             QtWidgets.QHeaderView.setResizeMode