virtio: fix virtqueue_set_affinity() docs
Rewrite the comment for better grammar and clarity.
Fixes: 75a0a52be3c2 ("virtio: introduce an API to set affinity for a virtqueue")
Message-Id: <e317e91bd43b070e5eaec0ebbe60c5749d02e2dd.1763026134.git.mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>