usb: gadget: at91_udc: fix dt support

commit 9c6d196d5aa35e07482f23c3e37755e7a82140e0 upstream.

Don't fail the initialization check for the platform_data
if there is avaiable an associated device tree node.

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>