SF: Fix two display identification bugs

1) getDisplayIdentificationData() was called on hotplug disconnect and
   not just on hotplug connect. The DisplayTransactionTest had a
   warning, and I've fixed the issue and made the test explicitly expect
   zero calls so it will fail instead.

2) One of the tests in DisplayIdentificationTest had a use after free,
   detected by enabling the address sanitizer on the unit test executable.

Bug: None
Test: Test passes with no errors or warnings
Change-Id: Iceda0d499d692991adfcbf5c772da736bd4a843f