usb: gadget: ncm: correct endianess conversion

Convert USB descriptor's fields to CPU byte order before using locally in USB
NCM gadget driver.

Tested on MIPS32 big-endian device.

Signed-off-by: Dmytro Milinevskyy <milinevskyy@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>