[mlir][linalg][bufferize] Fix insertion point InitTensorElimination

There was a bug where some of the OpOperands needed in the replacement op were not in scope.

It does not matter where the replacement op is inserted. Any insertion point is OK as long as there are no dominance errors. In the worst case, the newly inserted op will bufferize out-of-place. This is no worse than not eliminating the InitTensorOp at all.

Differential Revision: https://reviews.llvm.org/D117685