HID: sony: fix HID mapping for PS3 sixaxis controller

Commit f04d5140 (HID: driver for PS2/3 Buzz controllers) introduced
an input_mapping() callback, but set the return value to -1 to all devices
except the Buzz controllers. The result of this is that the Sixaxis input
device is not populated, making it useless.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>