account_voucher_comment/account_vouchersupplier_comment_view.xml

<?xml version="1.0"?>
<openerp>
    <data>
        <record id="account_vouchersupplier_comment_view" model="ir.ui.view">
            <field name="name">account.vouchersupplier.comment</field>
            <field name="model">account.voucher</field>
            <field name="inherit_id" ref="account_voucher.view_vendor_payment_form"/>
            <field name="arch" type="xml">
                <field name="journal_id" position="after">
                    <field name="comment_obs" attrs="{'readonly':False}"/>
                </field>
            </field>
        </record>

    </data>
</openerp>