UPSTREAM: Input: reset device timestamp on sync

We need to reset input device's timestamp on input_sync(), otherwise
drivers not using input_set_timestamp() will end up with a stale
timestamp after their clients consume first input event.

Bug: 150896413
Fixes: 3b51c44bd693 ("Input: allow drivers specify timestamp for input events")
Reported-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
(cherry picked from commit 4370b231d1001e0b560f82fd93616c7e54bd5fda)
Signed-off-by: Hridya Valsaraju <hridya@google.com>
Change-Id: I35b76cbed146a4ee8e021388eb7a68282daf9003