TouchInputMapper: Fix display association for POINTER mode

POINTER mode in TouchInputMapper is now only used for drawing tablets
and absolute mice; it is no longer used for touchpads. This means
TouchInputMapper can only work with an associated display, so ensure we
don't use the invalid displayId when generating events from these
devices.

Bug: 332683415
Test: Presubmit
Flag: EXEMPT bug fix
Change-Id: Ice0ee9be87d0582c553ef3743ac3f0d49a12c6ea