ath9k_htc: accept 1.x firmware newer than 1.3

Since the firmware has been open sourced, the minor version has been
bumped to 1.4 and the API/ABI will stay compatible across further 1.x
releases.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Cc: stable@vger.kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>