cpufreq: governor: Clean up load-related computations

Clean up some load-related computations in dbs_check_cpu() and
cpufreq_governor_start() to get rid of unnecessary operations and
type casts and make the code easier to read.

No functional changes.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>