proc: fix proc-empty-vm test with vsyscall

* fix embarassing /proc/*/smaps test bug due to a typo in variable name
  it tested only the first line of the output if vsyscall is enabled:

  	ffffffffff600000-ffffffffff601000 r-xp ...

  so test passed but tested only VMA location and permissions.

* add "KSM" entry, unnoticed because (1)

* swap "r-xp" and "--xp" vsyscall test strings,
  also unnoticed because (1)

Link: https://lkml.kernel.org/r/76f42cce-b1ab-45ec-b6b2-4c64f0dccb90@p183


Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Tested-by: Swarup Laxman <Kotikalapudi&lt;swarupkotikalapudi@mail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>