/proc/pagetypeinfo: fix output for memoryless nodes

on memoryless node, /proc/pagetypeinfo is displayed slightly funny output.
this patch fix it.

output example (header is outputed, but no data is outputed)
--------------------------------------------------------------
Page block order: 14
Pages per block:  16384

Free pages count per migrate type at order       0      1      2      3      4      5    \
  6      7      8      9     10     11     12     13     14     15     16

Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
Page block order: 14
Pages per block:  16384

Free pages count per migrate type at order       0      1      2      3      4      5    \
  6      7      8      9     10     11     12     13     14     15     16

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>