Use the USB-interface rather than parent USB-device device, which is
what this driver binds to, when registering the nci device.

Note that using the right device is important when dealing with device-
managed resources as the interface can be unbound independently of the
parent device.

Also note that private device pointer had already been set by
nfcmrvl_nci_register_dev() so the redundant assignment can therefore be
removed.
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>