tools lib traceevent: Fix time stamp rounding issue

tools lib traceevent: Fix time stamp rounding issue

When rounding to microseconds, if the timestamp subsecond is between
.999999500 and .999999999, it is rounded to .1000000, when it should
instead increment the second counter due to the overflow.

For example, if the timestamp is 1234.999999501 instead of seeing:

  1235.000000

we see:

  1234.1000000

Signed-off-by: Chaos.Chen <rainboy1215@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20160209204236.824426460@goodmis.org
[ fixed incrementing "secs" instead of decrementing it ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>