usb: gadget: udc: atmel: Minor code cleanup

Minor code cleanup based on feedback received on mailinglist.

Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Cristian Birsan <cristian.birsan@microchip.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>