usb: gadget: fsl_udc: fix the usage of udc->max_ep

usb: gadget: fsl_udc: fix the usage of udc->max_ep

The max_ep is the number of endpoint * 2.

But in dtd_complete_irq, it does again * 2, it will deference wrong memory
after scanning max_ep - 1.

The another similar problem is at USB_REQ_SET_FEATURE (the pipe number
should be 0 and max_ep - 1).

Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Matthieu castet <matthieu.castet@parrot.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>