Christoph noted that the documentation doesn't tell in what unit the
lockstat times are reported, ammend this.
Reported-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>