am 4c1dfc62: Fix a critical underflow in the touch calibration. This is a cherry-pick of Iacc746e1cc97bf3 Bug: 5629373 Change-Id: Ia198fe5e82b9e7fb801d9bae65cf9c6bbbd1befa

* commit '4c1dfc62c8d59c7503d3635c96a4c1582f9d9e8a':
  Fix a critical underflow in the touch calibration. This is a cherry-pick of Iacc746e1cc97bf3 Bug: 5629373 Change-Id: Ia198fe5e82b9e7fb801d9bae65cf9c6bbbd1befa