b43: fix frequency reported on G-PHY with /new/ firmware

b43: fix frequency reported on G-PHY with /new/ firmware

Support for firmware rev 508+ was added years ago, but we never noticed
it reports channel in a different way for G-PHY devices. Instead of
offset from 2400 MHz it simply passes channel id (AKA hw_value).

So far it was (most probably) affecting monitor mode users only, but
the following recent commit made it noticeable for quite everybody:

commit ec75c64989f65d720eac8ed859d570de55f4eefa
Author: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Date:   Tue Mar 4 16:50:13 2014 +0200

    cfg80211/mac80211: ignore signal if the frame was heard on wrong channel

Reported-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Cc: stable@vger.kernel.org
Tested-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>