COMPMID-556 Add macro for checking graph's tensor object

Change-Id: I1de1c2932c9906b23b49e18bd82c173846d98723
Reviewed-on: http://mpd-gerrit.cambridge.arm.com/93860
Tested-by: Kaizen <jeremy.johnson+kaizengerrit@arm.com>
Reviewed-by: Anthony Barbier <anthony.barbier@arm.com>
Reviewed-by: Pablo Tello <pablo.tello@arm.com>
diff --git a/arm_compute/graph/ITensorObject.h b/arm_compute/graph/ITensorObject.h
index 61be286..a922dd5 100644
--- a/arm_compute/graph/ITensorObject.h
+++ b/arm_compute/graph/ITensorObject.h
@@ -61,7 +61,8 @@
      *
      * @return Tensor
      */
-    virtual ITensor *tensor() = 0;
+    virtual ITensor       *tensor()       = 0;
+    virtual const ITensor *tensor() const = 0;
     /** Return the target that this tensor is pinned on
      *
      * @return Target of the tensor