ath9k: fix AR5416 access GPIO warning

ath9k: fix AR5416 access GPIO warning

The warning was seen on AR5416 chip, which invoke ath9k_hw_gio_get()
before the GPIO initialized correctly.

    WARNING: CPU: 1 PID: 1159 at ~/drivers/net/wireless/ath/ath9k/hw.c:2776 ath9k_hw_gpio_get+0x148/0x1a0 [ath9k_hw]
    ...
    CPU: 1 PID: 1159 Comm: systemd-udevd Not tainted 4.7.0-rc7-aptosid-amd64 #1 aptosid 4.7~rc7-1~git92.slh.3
    Hardware name:                  /DH67CL, BIOS BLH6710H.86A.0160.2012.1204.1156 12/04/2012
      0000000000000286 00000000f912d633 ffffffff81290fd3 0000000000000000
      0000000000000000 ffffffff81063fd4 ffff88040c6dc018 0000000000000000
      0000000000000002 0000000000000000 0000000000000100 ffff88040c6dc018
    Call Trace:
      [<ffffffff81290fd3>] ? dump_stack+0x5c/0x79
      [<ffffffff81063fd4>] ? __warn+0xb4/0xd0
      [<ffffffffa0668fb8>] ? ath9k_hw_gpio_get+0x148/0x1a0 [ath9k_hw]

Signed-off-by: Miaoqing Pan <miaoqing@codeaurora.org>
Reported-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>
Tested-by: Stefan Lippers-Hollmann <s.l-h@gmx.de>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>