HID: nintendo: Set phys property of input device based on HID phys

While the MAC address the uniq identifier is set to (cf. commit
14252473

 ("HID: nintendo: set controller uniq to MAC")) is certainly
unique, the physical location can be more helpful in user interfaces.  The
underlying hid_device already provides a suitable value, so we can simply
reuse this here.

Signed-off-by: Thomas Schneider <qsx@chaotikum.eu>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>