Make sure AmbiguousGestureMultiplier could start from 1

If a motion event classified CLASSIFICATION_AMBIGUOUS_GESTURE, it would
multiplied the AmbiguousGestureMultiplier from configuration for the
touch slop, we have to make sure this value should be start from 1 or
the touch slop could be zero and click action may fail.

Bug: 155160957
Test: manual
Change-Id: I61e1262b4f3de61214297b678956cc14fa2f24ef