[MAC80211]: fix warnings introduced by the doc patches

This fixes a warning about NUM_IEEE80211_MODES missing
in a switch statement. Intentionally do not add a default
case so we get warnings at these places if we need to add
new modes.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Michael Wu <flamingice@sourmilk.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>