ath9k_hw: AR9003 does not have AR_RC_AHB skip its setting

AR9003 does not have a reset control for AHB.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>