rt2x00: Fix rfkill polling prior to interface start.

We need to program the rfkill switch GPIO pin direction to input at
device initialization time, not only when the interface is brought up.
Doing this only when the interface is brought up could lead to rfkill
detecting the switch is turned on erroneously and inability to create
the interface and bringing it up.

Reported-and-tested-by: Andreas Messer <andi@bastelmap.de>
Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Cc: <stable@vger.kernel.org>
Acked-by: Ivo Van Doorn <ivdoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>