mac80211: fix docbook

Fix a small problem in the documentation for
ieee80211_request_smps, and a now erroneous
inclusion of enum ieee80211_key_alg, which no
longer exists after the change to ciphers.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>