usb: gadget: udc: atmel: remove unnecessary & operation

Now that usb_endpoint_maxp() only returns the lowest
11 bits from wMaxPacketSize, we can remove the &
operation from this driver.

Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: <linux-usb@vger.kernel.org>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>