Don't reset changed_ to false every time PerformSpaceToBatchOnConvolution is called.
Don't reset changed_ to false every time PerformSpaceToBatchOnConvolution is called.

For example after PropagateOnUsers is called, new broadcast instructions are added so changed_ should be true. This makes it possible for the hlo module to be saved after this pass has rewrote or added new hlo instructions (module pertaining to the pass is only saved if there are changes).
