Fix rsGetElementAt* for half

* Use the correct vector size for half3 and half4
* Directly return the result for rsGetElementAtImpl_half3 instead of the
  pointer argument to store the return value
* Add TBAA metadata to a load

Change-Id: Ia728bbb3f7cc3b02c0d6307bd48122f3c7d9cd44
2 files changed