[processing] fix axis orientation in the Vector Scatterplot alg (fix #12705)

Author: alexbruy

python/plugins/processing/algs/qgis/VectorLayerScatterplot.py

@@ -62,8 +62,8 @@ def defineCharacteristics(self):
     def processAlgorithm(self, progress):
         layer = dataobjects.getObjectFromUri(
             self.getParameterValue(self.INPUT))
-        xfieldname = self.getParameterValue(self.YFIELD)
-        yfieldname = self.getParameterValue(self.XFIELD)
+        xfieldname = self.getParameterValue(self.XFIELD)
+        yfieldname = self.getParameterValue(self.YFIELD)
 
         output = self.getOutputValue(self.OUTPUT)