mm/vmscan: don't use NUMA_NO_NODE as indicator of page on different node

mm/vmscan: don't use NUMA_NO_NODE as indicator of page on different node

Now we are sure there is at least one page on page_list, so it is safe to
get the nid of it.  This means it is not necessary to use NUMA_NO_NODE as
an indicator for the beginning of iteration or a page on different node.

Link: https://lkml.kernel.org/r/20220429014426.29223-2-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>