[mlir][Linalg] Make printer/parser have the same behavior.

[mlir][Linalg] Make printer/parser have the same behavior.

The parser of generic op did not recognize the output from mlir-opt when there
are multiple outputs. One would wrap the result types with braces, and one would
not. The patch makes the behavior the same.

Reviewed By: mravishankar

Differential Revision: https://reviews.llvm.org/D104256