The driver forgets to call unregister_pernet_subsys() in the error path
of cma_init().
Add the missed call to fix it.

Fixes: 4be74b42 ("IB/cma: Separate port allocation to network namespaces")
Signed-off-by: NChuhong Yuan <hslester96@gmail.com>
Reviewed-by: NParav Pandit <parav@mellanox.com>
Link: https://lore.kernel.org/r/20191206012426.12744-1-hslester96@gmail.comSigned-off-by: NDoug Ledford <dledford@redhat.com>