Revert "sched/psi: Optimize psi_group_change() cpu_clock() usage"

This reverts commit c1cbee3a which is
commit 570c8efd upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I0638e80c5c062251f406539143d77f90fa531df4
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>