backends/iommufd: Get rid of qemu_open_old()

backends/iommufd: Get rid of qemu_open_old()

For qemu_open_old(), osdep.h said:

> Don't introduce new usage of this function, prefer the following
> qemu_open/qemu_create that take an "Error **errp".

So replace qemu_open_old() with qemu_open().

Cc: Yi Liu <yi.l.liu@intel.com>
Cc: Eric Auger <eric.auger@redhat.com>
Cc: Zhenzhong Duan <zhenzhong.duan@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Yi Liu <yi.l.liu@intel.com>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>