usb: pxa27x_udc: remove unused function argument

We get a warning for this when building with W=1 because the
argument gets assigned to something else but never read:

drivers/usb/gadget/udc/pxa27x_udc.c: In function 'stop_activity':
drivers/usb/gadget/udc/pxa27x_udc.c:1828:74: error: parameter 'driver' set but not used [-Werror=unused-but-set-parameter]

This remove the argument entirely.

Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>