rq_stats: changing the show function for sysfs entry def_timer_ms

The computation done in sysfs show function show_def_timer_ms is
already happening in function def_work_fn. Since there can be a
time gap between when the computation is done in def_work_fn to
when it is done in show_def_timer_ms; the correct computation
is the one done in def_work_fn. Therefore removing the extra
computation from show_def_timer_ms.

Change-Id: I91f7d3f48d7c22282a5709432775a63e448c2fe3
Signed-off-by: Amar Singhal <asinghal@codeaurora.org>