HID: logitech-hidpp: avoid unintended fall-through

Add a return to avoid a fall-through. Introduced in commit
57ac86cf

 ("HID: logitech-hidpp: add
support of the first Logitech Wireless Touchpad").

Signed-off-by: Peter Wu <peter@lekensteyn.nl>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>