[FIX] mrp: add product_uom_category for domain

Without the product_uom_category_id set you cannot edit this tree view. There is a domain [('category_id', '=', product_uom_category_id)] triggered from this view whcich is not fulfilled if we do not have the field set in the tree.

closes odoo/odoo#39551

Signed-off-by: Simon Lejeune (sle) <sle@openerp.com>