[FIX] point_of_sale: Enable Price Control

Steps to reproduce the bug:
POS -> Settings -> Enable Price Control.
Login with user with POS -> Manager rights
Open POS Session.

Bug: Price Option was disable.

opw:784422

addons/point_of_sale/static/src/js/models.js

@@ -276,6 +276,7 @@ exports.PosModel = Backbone.Model.extend({
                 // replace the current user with its updated version
                 if (user.id === self.user.id) {
                     self.user = user;
+                    self.set_cashier(user);
                 }
             }
             self.users = pos_users;