cpufreq: interactive: Revert DEFAULT_TIMER_SLACK change

Was testing 3.5 * DEFAULT_TIMER_RATE. Revert back to 4, was causing
premature app closures

Change-Id: Iab7c416d05ba416192f33e47694a6d0006e04351
Signed-off-by: bmc08gt <bmc08gt.teamb00sted@gmail.com>