cpuidle: ladder: fix ladder_do_selection() kernel-doc

make C=1 reports:

warning: Function parameter or struct member 'dev' not described in 'ladder_do_selection'

Document 'dev' for this function.
Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpuidle/governors/ladder.c

@@ -44,6 +44,7 @@ static DEFINE_PER_CPU(struct ladder_device, ladder_devices);
 
 /**
  * ladder_do_selection - prepares private data for a state change
+ * @dev: the CPU
  * @ldev: the ladder device
  * @old_idx: the current state index
  * @new_idx: the new target state index