Fix dangerous unsafe_get() in SensorRecord

Change raw pointers to wp<> and constify relevant lines in
SensorRecord.

Bug: 30261110

Change-Id: I7f28c593366af44192991061fa5f71cf925b22a8
(cherry picked from commit ded526e8c3539b5986b46dffc1ff8ab15d7da570)
6 files changed