ath5k: fix scanning in AR2424

AR5K_PHY_PLL_40MHZ_5413 should not be ORed with AR5K_PHY_MODE_RAD_RF5112
for 5 GHz channels.

The incorrect PLL value breaks scanning in the countries where 5 GHz
channels are allowed.

Signed-off-by: Pavel Roskin <proski@gnu.org>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>