doc: trace: fix reference to cpuidle documentation file

Old cpuidle/sysfs.txt file was replaced in aa5eee35. So, refer to
an updated file.

Fixes: aa5eee35 (Documentation: admin-guide: PM: Add cpuidle document)
Signed-off-by: Otto Sabart <ottosabart@seberm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/trace/coresight-cpu-debug.txt

@@ -165,7 +165,7 @@ Do some work...
 The same can also be done from an application program.
 
 Disable specific CPU's specific idle state from cpuidle sysfs (see
-Documentation/cpuidle/sysfs.txt):
+Documentation/admin-guide/pm/cpuidle.rst):
 # echo 1 > /sys/devices/system/cpu/cpu$cpu/cpuidle/state$state/disable