[FIX] l10n_be: allow more than 120 periods

The widget selection only shows the first 120 results.
The selection was most likely set to avoid creating new entries but it can be
done with an option tag. This allows to use the search on many2one fields.

opw-677908

addons/l10n_be/wizard/l10n_be_account_vat_declaration_view.xml

@@ -9,7 +9,7 @@
                 <form string="Periodical VAT Declaration">
                     <group>
                         <group string="Declare Periodical VAT">
-                            <field name="period_id" widget="selection"/>
+                            <field name="period_id" nocreate="True"/>
                             <field name="tax_code_id" string="Company" widget="selection" groups="base.group_multi_company"/>
                         </group>
                         <group string="Advanced Options">