vfio/iommufd: Make iommufd_cdev_*() return bool

vfio/iommufd: Make iommufd_cdev_*() return bool

This is to follow the coding standand to return bool if 'Error **'
is used to pass error.

The changed functions include:

iommufd_cdev_kvm_device_add
iommufd_cdev_connect_and_bind
iommufd_cdev_attach_ioas_hwpt
iommufd_cdev_detach_ioas_hwpt
iommufd_cdev_attach_container
iommufd_cdev_get_info_iova_range

After the change, all functions in hw/vfio/iommufd.c follows the
standand.

Suggested-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>