When trying to destroy platform data after destruction of SMbus companion,
we need to make sure that we are actually dealing with an SMB companion
device, and not some random I2C client device.

Fixes: 8eb92e5c ("Input: psmouse - add support for SMBus companions")
Reported-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Tested-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>