[FIX] mrp,stock: use correct qty to backorder in MO simplified view

The problem arises when a user creates a backorder for a MO after
registering overconsumption of some components through the simplified view.
The quantities of the components of the new backordered MO are then wrong.
Components that were over consumed in the first MO will have smaller
quantities in the new MO, the difference being the amount over consumed.
This problem does not appear in the case of the Tablet View where a proper
recalculation of quantities is done.

closes odoo/odoo#64911

Signed-off-by: Arnold Moyaux <amoyaux@users.noreply.github.com>