lockdep: Simplify lock_stat seqfile code

- make ls_next() call ls_start()
- remove redundant code in lock_stat_release()

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <4A88ED6B.6030602@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>