[FIX] hr_holidays: fix ambiguous column

Use fully qualified names as columns in related table can have a same name
and this query could raise an error.

Like the one below error below was shown in 18.0
```
psycopg2.errors.AmbiguousColumn: column reference "state" is ambiguous
LINE 3:                             AND state = 'validate'
```

closes odoo#193568

Signed-off-by: Jurgen Gjini (jugj) <[email protected]>

Author: asno-odoo

addons/hr_holidays/models/res_users.py

@@ -54,7 +54,7 @@ def _get_on_leave_ids(self, partner=False):
                             AND hr_leave.state = 'validate'
                             AND hr_leave.active = 't'
                             AND res_users.active = 't'
-                            AND date_from <= %%s AND date_to >= %%s''' % field, (now, now))
+                            AND hr_leave.date_from <= %%s AND hr_leave.date_to >= %%s''' % field, (now, now))
         return [r[0] for r in self.env.cr.fetchall()]
 
     def _clean_leave_responsible_users(self):