HID: add missing \n to end of dev_warn messages

Trival fix, dev_warn messages are missing a \n, so add it.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>