[mlir][tosa] Rename the result of MATMUL from c to output (llvm#129274)

This renames the output of TOSA MatMul operator from `c` to `output`
to align to TOSA spec

Co-authored-by: TatWai Chong <[email protected]>

Author: Tai78641

mlir/include/mlir/Dialect/Tosa/IR/TosaOps.td

@@ -301,7 +301,7 @@ def Tosa_MatMulOp : Tosa_InferShapedTypeOp<"matmul"> {
   );
 
   let results = (outs
-    Tosa_Tensor3D:$c
+    Tosa_Tensor3D:$output
   );
 
   list<Availability> availability = [