[PATCH] bcm43xx: fix for 4309

BCM4309 devices aren't working properly as A PHYs aren't supported
yet, but we probe 802.11a cores anyway. This fixes it, while still
allowing for A PHY code to be developed in the future.

Signed-off-by: Stefano Brivio <stefano.brivio@polimi.it>
Signed-off-by: John W. Linville <linville@tuxdriver.com>