wifi: iwlwifi: Add short description to enum iwl_power_scheme

The kernel-doc script flagged the following:

drivers/net/wireless/intel/iwlwifi/mvm/mvm.h:130: warning: missing initial short description on line:
 * enum iwl_power_scheme
1 warnings as Errors

Add a short description to address this warning.

Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20250319-iwl_power_scheme-kdoc-v1-1-2033ae38b178@oss.qualcomm.com


Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>