selftests/proc: fixup proc-empty-vm test after KSM changes

/proc/${pid}/smaps_rollup is not empty file even if process's address
space is empty, update the test.

Link: https://lkml.kernel.org/r/725e041f-e9df-4f3d-b267-d4cd2774a78d@p183
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Stefan Roesch <shr@devkernel.io>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: Alexey Dobriyan

tools/testing/selftests/proc/proc-empty-vm.c

@@ -267,6 +267,7 @@ static const char g_smaps_rollup[] =
 "Private_Dirty:         0 kB\n"
 "Referenced:            0 kB\n"
 "Anonymous:             0 kB\n"
+"KSM:                   0 kB\n"
 "LazyFree:              0 kB\n"
 "AnonHugePages:         0 kB\n"
 "ShmemPmdMapped:        0 kB\n"