Ok you can try the below approach:

Declare
  v_item inventory.item%type := :p2_item;
  v_qty number := :p2_saleqty;
  /* get the quantity available date wise */
  Cursor c_item
   is
  Select qty_in_hand, rec_date
   from inventory where item = v_item
  order by rec_date asc;
Begin
  for c in c_item loop
     if c.qty_in_hand >= v_qty then
        Update inventory
           set qty_in_hand = qty_in_hand - v_qty
          where item = v_item and rec_date = c.rec_date;
          v_qty := 0;
     else
        Update inventory
          set qty_in_hand = qty_in_hand - c.qty_in_hand
        where item = v_item and rec_date = c.rec_date;
        v_qty := v_qty - c.qty_in_hand;
     end if;
     if v_qty = 0 then
         exit;
     end if;
  end loop;
  commit;
End;