HID: logitech-hidpp: bail out if wtp_connect fails

If wtp_connect() fails, that means most of the time that the device has
been disconnected. Subsequent attempts to contact the device will fail
too, so it's simpler to bail out earlier.

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