[FIX] partner_autocomplete: stop comparing apples and oranges

If no country is specified on a partner, self.country_id is
res.country() and partner_country_code contains res.country(). In the
next line the code was comparing `res.country()` with `'BE'`, raising
a warning.

closes odoo/odoo#53966

Signed-off-by: Martin Trigaux (mat) <mat@odoo.com>