ath9k: Remove useless opmode check

The opmode is verified to be NL80211_IFTYPE_STATION
before calling ath9k_set_assoc_state().

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>