Cleanup: use POINTER_FROM_INT for PyGetSetDef definitions

This makes it clear '(void *)0' represents a zero index instead of
a value that's typically nullptr when ignored.

source/blender/python/mathutils/mathutils_Quaternion.cc

@@ -1551,22 +1551,22 @@ static PyGetSetDef Quaternion_getseters[] = {
      (getter)Quaternion_axis_get,
      (setter)Quaternion_axis_set,
      Quaternion_axis_doc,
-     (void *)0},
+     POINTER_FROM_INT(0)},
     {"x",
      (getter)Quaternion_axis_get,
      (setter)Quaternion_axis_set,
      Quaternion_axis_doc,
-     (void *)1},
+     POINTER_FROM_INT(1)},
     {"y",
      (getter)Quaternion_axis_get,
      (setter)Quaternion_axis_set,
      Quaternion_axis_doc,
-     (void *)2},
+     POINTER_FROM_INT(2)},
     {"z",
      (getter)Quaternion_axis_get,
      (setter)Quaternion_axis_set,
      Quaternion_axis_doc,
-     (void *)3},
+     POINTER_FROM_INT(3)},
     {"magnitude",
      (getter)Quaternion_magnitude_get,
      (setter) nullptr,