vdpa/mlx5: Fix oversized null mkey longer than 32bit

create_user_mr() has correct code to count the number of null keys
used to fill in a hole for the memory map. However, fill_indir()
does not follow the same to cap the range up to the 1GB limit
correspondingly. Fill in more null keys for the gaps in between,
so that null keys are correctly populated.

Fixes: 94abbccd ("vdpa/mlx5: Add shared memory registration code")
Cc: stable@vger.kernel.org
Reported-by: Cong Meng <cong.meng@oracle.com>
Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Acked-by: Eugenio Pérez <eperezma@redhat.com>
Message-Id: <20250220193732.521462-2-dtatulea@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>