Input: psmouse - add a newline when printing 'proto' by sysfs

When I cat parameter 'proto' by sysfs, it displays as follows. It's
better to add a newline for easy reading.

root@syzkaller:~# cat /sys/module/psmouse/parameters/proto
autoroot@syzkaller:~#

Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Link: https://lore.kernel.org/r/20200720073846.120724-1-wangxiongfeng2@huawei.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>