ath9k_hw: fix power for the HT40 duplicate frames

With AR9003 at about ~ 10 feet from an AP that uses RTS / CTS you
will be able to associate but not not get data through given that
the power for the rates used was set too low. This increases the
power and permits data connectivity at longer distances from
access points when connected with HT40. Without this you will not
get any data through when associated to APs configured in HT40
at about more than 10 feet away.

Cc: stable@kernel.org
Cc: Fiona Cain <fcain@atheros.com>
Cc: Zhen Xie <Zhen.Xie@Atheros.com>
Cc: Kathy Giori <kathy.giori@atheros.com>
Cc: Neha Choksi <neha.choksi@atheros.com>
Cc: Wayne Daniel <wayne.daniel@atheros.com>
Cc: Gaurav Jauhar <gaurav.jauhar@atheros.com>
Cc: Samira Naraghi <samira.naraghi@atheros.com>
CC: Ashok Chennupati <ashok.chennupati@atheros.com>
Cc: Lance Zimmerman <lance.zimmerman@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>