sched: cpufreq: Use sched_clock instead of rq_clock when updating schedutil

rq_clock may not be updated often enough for schedutil or other
cpufreq governors to work correctly when it's passed as the
timestamp for a load report. Use sched_clock instead.

Change-Id: I745b727870a31da25f766c2c2f37527f568c20da
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>