virtio-balloon: Fix page-poison subsection name

virtio-balloon: Fix page-poison subsection name

The subsection name for page-poison was typo'd as:

  vitio-balloon-device/page-poison

Note the missing 'r' in virtio.

When we have a machine type that enables page poison, and the guest
enables it (which needs a new kernel), things fail rather unpredictably.

The fallout from this is that most of the other subsections fail to
load, including things like the feature bits in the device, one
possible fallout is that the physical addresses of the queues
then get aligned differently and we fail with an error about
last_avail_idx being wrong.
It's not obvious to me why this doesn't produce a more obvious failure,
but virtio's vmstate loading is a bit open-coded.

Fixes: 7483cbbaf82 ("virtio-balloon: Implement support for page poison reporting feature")
bz: https://bugzilla.redhat.com/show_bug.cgi?id=1984401
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20210914131716.102851-1-dgilbert@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>