ath9k: Fix buffer overflow error

The commit "ath9k: stomp audio profiles on weak signal
strength" failed to take care of new stomp type while
programming concurrent tx priority. That leads to array
index out of bounds access.

drivers/net/wireless/ath/ath9k/btcoex.c:414
        ath9k_hw_btcoex_set_concur_txprio()
               error: buffer overflow 'stomp_txprio' 4 <= 4

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Rajkumar Manoharan <rmanohar@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>