cpufreq: interactive: add check for delta_idle and delta_time

While a CPU is in idle on SMP systems, CPU frequency could be changed by other
CPUs and then delta_idle of the currently idled CPU might be greater than
delta_time of the CPU. It would end up computing a extremely large active_time
and cpu load.

Change-Id: I3e4c6ef1ad794eec49ed379c0c50fa727fd6ad28
Signed-off-by: Minsung Kim <ms925.kim@samsung.com>
Signed-off-by: Francisco Franco <franciscofranco.1990@gmail.com>

Conflicts:
	drivers/cpufreq/cpufreq_interactive.c