ath9k: fix ath9k_hw_gpio_get() to return 0 or 1 on success

ath9k: fix ath9k_hw_gpio_get() to return 0 or 1 on success

Commit f81ada921b34 ("ath9k: make GPIO API to support both of WMAC and
SOC") refactored ath9k_hw_gpio_get() to support both WMAC and SOC GPIOs,
changing the return on success from 1 to BIT(gpio). This broke some callers
like ath_is_rfkill_set(). This doesn't fix any known bug in mainline at the
moment, but should be fixed anyway.

Instead of fixing all callers, change ath9k_hw_gpio_get() back to only
return 0 or 1.

Fixes: f81ada921b34 ("ath9k: make GPIO API to support both of WMAC and SOC")
Cc: <stable@vger.kernel.org> # v4.7+
Signed-off-by: Matthias Schiffer <mschiffer@universe-factory.net>
[kvalo@qca.qualcomm.com: mention that doesn't fix any known bug]
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>