Input: serio - trivial documentation fix

In include/linux/serio.h two different define-series are documented as
"Serio types". However the second series contains defines for the
different protocols.

Signed-off-by: Niels de Vos <niels.devos@wincor-nixdorf.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>