rt2x00: Rework rt61 antenna selection.

This patch changes rt61 antenna selection again. It helps at least with the
rt61 pci card in my box, I hope I haven't broken behaviour on other RF chips.
RF 2529 antenna setup is incomplete, we need to at code for diversity when we
figure out how it is done properly.

Signed-off-by: Mattias Nissler <mattias.nissler@gmx.de>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>