staging: nvec: ps2: let the start/stop streaming commands be called by the start/stop functions of serio

Instead of executing these commands during open/close, the start/stop
event of the serio device seem to be more appropiete.
Signed-off-by: Marc Dietrich <marvin24@gmx.de>
Signed-off-by: Julian Andres Klode <jak@jak-linux.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>