ath9k_hw: Fix number of GPIO pins for AR9287/9300

this patch fixes the assumption of maximum number of GPIO pins present
in AR9287/AR9300. this fix is essential as we might encounter some
functionality issues involved in accessing the status of GPIO pins which
are all incorrectly assumed to be not within the range of max_num_gpio
of AR9300/AR9287 chipsets

Cc: stable@kernel.org
Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>