vdpa/mlx5: Fix umem sizes assignments on VQ create

Fix copy paste bug assigning umem1 size to umem2 and umem3. The issue
was discovered when trying to use a 1:1 MR that covers the entire
address space where firmware complained that provided sizes are not
large enough. 1:1 MRs are required to support virtio_vdpa.

Fixes: 1a86b377

 ("vdpa/mlx5: Add VDPA driver for supported mlx5 devices")
Signed-off-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20210530090317.8284-1-elic@nvidia.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>