ath9k: fix mci_is_enabled utility

During driver stop, btcoex is disabled and also btcoex_hw.enabled
is set to false. Afterwards mci_is_enabled returns false so that
BT is not gaining SPDT control on WLAN sleep. Fix that.

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