Input: adafruit-seesaw - only report buttons that changed state

If a button has not changed its state when we poll the device the
driver does not need to report it. While duplicate events will be
filtered out by the input core anyway we can do it very cheaply
directly in the driver.

Link: https://lore.kernel.org/r/ZZ-U_bmZpIdoYA6c@google.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>