usb: gadget: nokia: convert to new interface of f_phonet

use the new interface which will allow us to deprecate the
legacy way of binding functions.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>