init: Fix comment

Apparently "pid-1" confuses people...

Requested-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: torvalds@linux-foundation.org
Cc: randy.dunlap@oracle.com
Cc: Ilya Loginov <isloginov@gmail.com>
LKML-Reference: <1277887031.1868.82.camel@laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>