wacom: Correct order of area calibration values

Commit cf408c27 changed how the values stored in the "area" key were
calculated in order be compatible with its updated schema. Unfortunately,
it overlooked the fact that updated schema also changed the order of the
values from "left, top, right, bottom" to "left, right, top, bottom".
Because of this, corrections intended to be applied to the top and right
screen edges were swapped. This can cause a noticible cursor offset to
occur after finishing calibration.

https://bugzilla.gnome.org/show_bug.cgi?id=784009