Rename the result of MATMUL from c to output

Term alignment between the spec and dialect.

Change-Id: I8dd88e4e4d9393903f195fde4fee2d22fa1acb00

Author: tatwaichong

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 = [