vdpa/mlx5: Restore the hardware used index after change map

[ Upstream commit b35ccebe ]

When a change of memory map occurs, the hardware resources are destroyed
and then re-created again with the new memory map. In such case, we need
to restore the hardware available and used indices. The driver failed to
restore the used index which is added here.

Also, since the driver also fails to reset the available and used
indices upon device reset, fix this here to avoid regression caused by
the fact that used index may not be zero upon device reset.

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/20210204073618.36336-1-elic@nvidia.com
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>