With scale-invariant usage tracking get_cpu_usage() should never return
a usage above the current compute capacity of the cpu (capacity_curr).
The scaling of the utilization tracking contributions should generally
cause the cpu utilization to saturate at capacity_curr, but it may
temporarily exceed this value in certain situations. This patch changes
the cap from capacity_orig to capacity_curr.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>

Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>