ath5k: Fix radio identification on AR5424/2424

 *Fix radio chip identification on AR5424/2424 during ath5k_hw_attach
 *Try to assign an RF2413 radio on AR2424 for testing

 Changes-licensed-under: ISC

Signed-off-by: Nick Kossifidis <mickflemm@gmail.com>

Signed-off-by: John W. Linville <linville@tuxdriver.com>