cgroup/cpuset: fix a few kernel-doc warnings & coding style

Fix kernel-doc notation warnings:

kernel/cgroup/cpuset.c:1309: warning: Excess function parameter 'cpuset' description in 'update_parent_subparts_cpumask'
kernel/cgroup/cpuset.c:3909: warning: expecting prototype for cpuset_mem_spread_node(). Prototype was for cpuset_spread_node() instead

Also drop a blank line before EXPORT_SYMBOL_GPL() to be consistent
with kernel coding style.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Zefan Li <lizefan.x@bytedance.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: cgroups@vger.kernel.org
Signed-off-by: Tejun Heo <tj@kernel.org>