COMP: GetTimeVaryingVelocityField methods did not compile

The internal method call returns a raw pointer, which doesn't have the
GetPointer method. This error shows up on the dashboard with WrapITK.

Change-Id: If39b9e6b7c379636c75a2ce949f7a75d36954c3c
Merge topic 'FixTimeVaryingVelocityFieldTXGetPointer'

dd3c8e6 COMP: GetTimeVaryingVelocityField methods did not compile