nl80211: fix kernel-doc warning in the new SAE attribute

Format the items as a definition list, to avoid the warning
from the rst parsing.

Fixes: 9f0ffa41 ("cfg80211: Add support to configure SAE PWE value to drivers")
Link: https://lore.kernel.org/r/20201110094911.bb020e863aa0.I960caf90e2a8cc23f6bf9245d77524df6a4d8f37@changeid


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