wifi: cfg80211: reg: describe return values in kernel-doc

Describe the function return values in kernel-doc.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20230920211508.8b1e45c8bab8.I6dbae4f6dfe8f5352bc44565cc5131e73dd1873f@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>