rt2x00: Allow dynamic addition of PCI/USB IDs.

Both USB and PCI drivers allow a system administrator to dynamically add
USB/PCI IDs to the device table that a driver supports via the
/sys/bus/{usb,pci,pci_express}/drivers/<driver-name>/new_id files.

However, for the rt2x00 drivers using this method currently crashes the
system with a NULL pointer failure.

This is due to the set-up of rt2x00 where the probe functions require a
rt2x00_ops structure in the driver_info field of the probed device. As
this field is empty for the dynamically added devices this fails for
these devices.

Fix this by introducing driver-specific probe wrappers that do nothing
but calling the bus-specific probe functions with the rt2x00_ops structure
as an argument, rather than depending on the driver_info field.

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