rt2x00: Set PWR_PIN_CFG during initialization

Add PWR_PIN_CFG initialization for rt2800usb at the same point
as rt2800pci.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>