Input: serio - make serio_register_driver() return errors

Perform actual driver registration right in serio_register_driver()
instead of offloading it to kseriod and return proper error code to
callers if driver registration fails.

Note that driver <-> port matching is still done by kseriod to
speed up boot process since probing for PS/2 mice and keyboards
is pretty slow.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>