[mlir][Linalg] Fix reshape fusion to reshape the outs instead of creating new tensors.

When fusing tensor_reshape ops with generic/indexed_Generic op, new
linalg.init_tensor operations were created for the `outs` of the fused
op. While correct (technically) it is better to just reshape the
original `outs` operands and rely on canonicalization of init_tensor
-> tensor_reshape to achieve the same effect.

Differential Revision: https://reviews.llvm.org/D93774