ath9k_hw: check for MCI interrupt in get_isr

check for the condition of MCI interrupt being triggered and
appropriately obtain the values of MCI_INTERRUPT_RX_MSG_RAW and
MCI_INTERRUPT_RAW

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>