blktrace: fix timestamp in binary output

I found the timestamp is wrong:

 # echo bin > trace_option
 # echo blk > current_tracer
 # cat trace_pipe | blkparse -i -
 8,0    0        0     0.000000000   504  A   W ...
 ...
 8,7    1        0     0.008534097     0  C   R ...
            (should be 8.534097xxx)

user-space blkparse expects the timestamp to be nanosecond.
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Acked-by: Jens Axboe <jens.axboe@oracle.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/blktrace.c

@@ -1168,7 +1168,7 @@ static int blk_trace_synthesize_old_trace(struct trace_iterator *iter)
 	const int offset = offsetof(struct blk_io_trace, sector);
 	struct blk_io_trace old = {
 		.magic	  = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION,
-		.time     = ns2usecs(iter->ts),
+		.time     = iter->ts,
 	};
 
 	if (!trace_seq_putmem(s, &old, offset))