cpuset: remove unneeded NODEMASK_ALLOC() in cpuset_sprintf_memlist()

It's not necessary to copy cpuset->mems_allowed to a buffer allocated by
NODEMASK_ALLOC().  Just pass it to nodelist_scnprintf().

As spotted by Paul, a side effect is we fix a bug that the function can
return -ENOMEM but the caller doesn't expect negative return value.
Therefore change the return value of cpuset_sprintf_cpulist() and
cpuset_sprintf_memlist() from int to size_t.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Paul Menage <menage@google.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>