cpuidle: governors: teo: Use s64 consistently in teo_update()

cpuidle: governors: teo: Use s64 consistently in teo_update()

Two local variables in teo_update() are defined as u64, but their
values are then compared with s64 values, so it is more consistent
to use s64 as their data type.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/3026616.e9J7NaK4W3@rafael.j.wysocki