LLS: Fix NPE when backing service dies

The mService member variable should not be used directly as this can
cause an NPE if the backing service has died.  Instead, use the
getServiceGuarded() method which will take care of re-establishing
a connection to the backing service.

Change-Id: I290e69c07a2e56644de7a394543d1e36fac1cbcc
TICKET: CYNGNOS-2779
(cherry picked from commit 8c8601b9)