hw/vfio: fix iteration over global VFIODevice list

hw/vfio: fix iteration over global VFIODevice list

Commit 3d779abafe ("vfio/common: Introduce a global VFIODevice list")
introduced a global VFIODevice list, but forgot to update the list
element field name when iterating over the new list. Change the code
to use the correct list element field.

Fixes: 3d779abafe ("vfio/common: Introduce a global VFIODevice list")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2061
Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>