PM / devfreq: bimc-bwmon: Reduce margin for HW workaround

The HW workaround margin being too high reduces the effectiveness of the
interrupt. Try using a margin only when the measured bandwidth is too small
and risks the counter wrapping around multiple times before it's read.

Change-Id: Ic1e88ad360b2348dfb9ad314c42c1b0218010c1d
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>