devfreq: governor_cpubw_hwmon: Fix use of decay_rate

The decay rate tunable is used to compute the current averaged bandwidth
use, but the calculated value is never used. Fix this by using the
calculated averaged bandwidth instead of the instantaneous measured
bandwidth when computing the AB and IB votes.

Change-Id: Ic0ba3ce0d98f0ec185349fe6d86c4af26f222ff2
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>