vdpa/mlx5: Fix syntax errors in comments

Delete the redundant word 'is'.

Signed-off-by: Xiang wangx <wangxiang@cdjrlc.com>
Message-Id: <20220604143858.16073-1-wangxiang@cdjrlc.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>