ath9k_hw: take care of enabling MCI interrupts

ath9k_hw: take care of enabling MCI interrupts

enable MCI interrupt when ath9k_hw_enable_interrupts is called,
like during the completion of chip_reset before which the interrupts
are disabled

Cc: Wilson Tsao <wtsao@qca.qualcomm.com>
Cc: Senthil Balasubramanian <senthilb@qca.qualcomm.com>
Signed-off-by: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>