tools/vm/page_owner_sort: free memory before exit

Although when a process terminates, the kernel will removes memory
associated with that process, It's neither good style nor proper design to
leave it to kernel.  This patch free allocated memory before process exit.

Link: https://lkml.kernel.org/r/20221219164917.14132-1-iecedge@gmail.com


Signed-off-by: Jianlin Lv <iecedge@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>