sched: fix error path in cpupool_unassign_cpu_start()

sched: fix error path in cpupool_unassign_cpu_start()

In case moving away all domains from the cpu to be removed is failing
in cpupool_unassign_cpu_start() the error path is missing to release
sched_res_rculock.

The normal exit path is releasing domlist_read_lock instead (this is
currently no problem as the reference to the specific rcu lock is not
used by rcu_read_unlock()).

While at it indent the present error label by one space.

Reported-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Dario Faggioli <dfaggioli@suse.com>