usb: gadget: udc: atmel: fix debug output

The debug output now contains the wrong variable, as seen from the compiler
warning:

drivers/usb/gadget/udc/atmel_usba_udc.c: In function 'usba_ep_enable':
drivers/usb/gadget/udc/atmel_usba_udc.c:632:550: error: 'ept_cfg' may be used uninitialized in this function [-Werror=maybe-uninitialized]
  DBG(DBG_ERR, "%s: EPT_CFG = 0x%lx (maxpacket = %lu)\n",

This changes the debug output the same way as the other code.

Fixes: 741d2558 ("usb: gadget: udc: atmel: Update endpoint allocation scheme")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>