usb: gadget: pxa25x_udc: fix use-before-initialized bug

Fix use-before-initialized bug in pxa25x_udc driver.

Function usb_gadget_register_driver calls udc_disable,
and udc_disable calls pullup_off that uses dev->mach->udc_command.
But dev->mach is initialized in usb_gadget_register_driver after
calling udc_disable. This patch fixes the order of initialization.

Signed-off-by: Alex Sadovsky <Nable.MainInbox@googlemail.com>