Input: psmouse - store pointer to current protocol

Instead of storing only protocol "type" in pmsouse structure, store pointer
to the protocol structure, so that we have access to more data without
having to copy it over to psmouse structure.

Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>