ath9k: Fix some smatch warnings

drivers/net/wireless/ath/ath9k/hif_usb.c +135 hif_usb_mgmt_cb(6) warn:
variable dereferenced before check 'cmd'
drivers/net/wireless/ath/ath9k/btcoex.c +77 ath9k_hw_init_btcoex_hw(38)
error: buffer overflow 'ah->hw_gen_timers.gen_timer_index' 32 <=
2009813776

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