HID: ft260: do not populate /dev/hidraw device

Do not populate the /dev/hidraw on ft260 interfaces when the hid-ft260
driver is loaded.

$ sudo insmod hid-ft260.ko
$ ls /dev/hidraw*
/dev/hidraw0

$ sudo rmmod hid-ft260.ko
$ ls /dev/hidraw*
/dev/hidraw0  /dev/hidraw1  /dev/hidraw2

Reported-by: Enrik Berkhan <Enrik.Berkhan@inka.de>
Signed-off-by: Michael Zaidman <michael.zaidman@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>