sched: Fix legacy_freq argument in sched_get_task_cpu_cycles() tracepoint

The cpufreq based current frequency tracking is not supported in
the current code. Hence cpu_cur_freq() returns an incorrect value
which is printed as legacy_freq in sched_get_task_cpu_cycles()
trace point. Fix this by providing a new wrapper function
for current frequency based on arch_scale_freq_capacity().

Change-Id: Id9408d18392e17b657a4a807574bd1c57b482528
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>