get_stock_gl_code function called twice in the add_supp_invoice

@joe,  While adding new purchase invoice,  we are calling the add_supp_invoice function,  Which actually called get_stock_gl_code twice inside the entered_grns foreach, remove the second one.

    $stock_id = $entered_grn->item_code;
    $stock_gl_code = get_stock_gl_code($stock_id);

And the previous one already exist. to handle further gl codes.