b43: disable 5 GHz on G-PHY

This fixes regression introduced by adding some G-PHY devices to the
list of dual band devices. There is simply no support for 5 GHz on
G-PHY devices in b43. It results in:
WARNING: CPU: 0 PID: 79 at drivers/net/wireless/b43/phy_g.c:75 b43_gphy_channel_switch+0x125/0x130 [b43]()
b43-phy1 ERROR: PHY init: Channel switch to default failed

Regression was introduced by the following commit:

commit 773cfc50


Author: Rafał Miłecki <zajec5@gmail.com>
Date:   Mon May 19 23:18:55 2014 +0200

    b43: add more devices to the bands database

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>