Revert "Input: appletouch - fix integer overflow issue"

This reverts commit 04b4b88cca0ebe3813b4b6f014fb6a0db380b137.

While the original problem only caused a slight disturbance on the
edge of the touchpad, the commit above to "fix" it completely breaks
operation on some other models such as mine.

We'll sort this out separately, revert the patch for now.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>