The PXA2xx PCMCIA driver was registering a device_driver with the
platform_bus_type.  Unfortunately, this causes data outside the
device_driver structure to be dereferenced as if it were a
platform_driver structure, causing an oops.  Convert the PXA2xx
core driver to use the proper platform_driver structure.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>