tools/vm/page_owner_sort.c: check malloc() return

Link: https://lkml.kernel.org/r/20210506131402.10416-1-tangbin@cmss.chinamobile.com


Signed-off-by: Zhang Shengju <zhangshengju@cmss.chinamobile.com>
Signed-off-by: Tang Bin <tangbin@cmss.chinamobile.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>