ath9k_hw: fix parsing of HT40 5 GHz CTLs

The 5 GHz CTL indexes were not being read for all hardware
devices due to the masking out through the CTL_MODE_M mask
being one bit too short. Without this the calibrated regulatory
maximum values were not being picked up when devices operate
on 5 GHz in HT40 mode. The final output power used for Atheros
devices is the minimum between the calibrated CTL values and
what CRDA provides.

Cc: stable@kernel.org [2.6.27+]
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>