vdpa/mlx5: Fix double release of debugfs entry

commit f8a3db47 upstream.

The error path in setup_driver deletes the debugfs entry but doesn't
clear the pointer. During .dev_del the invalid pointer will be released
again causing a crash.

This patch fixes the issue by always clearing the debugfs entry in
mlx5_vdpa_remove_debugfs. Also, stop removing the debugfs entry in
.dev_del op: the debugfs entry is already handled within the
setup_driver/teardown_driver scope.

Cc: stable@vger.kernel.org
Fixes: f0417e72

 ("vdpa/mlx5: Add and remove debugfs in setup/teardown driver")
Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Gal Pressman <gal@nvidia.com>
Message-Id: <20230829174014.928189-2-dtatulea@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>