cpumask: update setup_node_to_cpumask_map() comments

node_to_cpumask() has been replaced by cpumask_of_node(), and wholly
removed since commit 29c337a0 ("cpumask: remove obsolete node_to_cpumask
now everyone uses cpumask_of_node").

So update the comments for setup_node_to_cpumask_map().

Signed-off-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>