cmhw: don't override BOARD_HARDWARE_CLASS

* use += instead of :=, so both the fusion3-common TapToWake and
  device-specific VibratorHW class get pulled in

Change-Id: Ide6f7aeece5d7e2710235bd828fa5b9bc9f61303
Merge remote-tracking branch 'upstream/cm-11.0' into kitkat