Some Logitech mice react to the magic knock like Elantech touchpad would.
This leads to those mice being misdetected as Elantech touchpads.  Add a
version query to elantech_detect() to distinguish the two.

[dtor@mail.ru:
 - lower severity of some messages - when we are not sure yet if
   device is Elantech or not not responding to knock is not an error.
]
Signed-off-by: Arjan Opmeer <arjan@opmeer.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>