Rename uom to unit in production split wizard

Closes #13263
(grafted from 261f623a7dd1fd54d6435082c82e6c24951fd560)

--HG--
branch : 7.0

modules/production_split/production.py

@@ -82,7 +82,7 @@ class SplitProduction(Wizard):
     def default_start(self, fields):
         return {
             'unit': self.record.unit.id,
-            'uom_category': self.record.uom.category.id,
+            'uom_category': self.record.unit.category.id,
             }
 
     def transition_split(self):