COMPMID-2194: Add identity function to NEActivationLayerKernel.cpp

Change-Id: Id9bc53722b7dfe277812e9e1d749ac4cea35260a
Signed-off-by: Usama Arif <usama.arif@arm.com>
Reviewed-on: https://eu-gerrit-1.euhpc.arm.com/184712
Tested-by: bsgcomp <bsgcomp@arm.com>
Reviewed-by: Gian Marco Iodice <gianmarco.iodice@arm.com>
Reviewed-on: https://review.mlplatform.org/c/1143
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Tested-by: Georgios Pinitas <georgios.pinitas@arm.com>
diff --git a/tests/validation/reference/ActivationLayer.h b/tests/validation/reference/ActivationLayer.h
index 77b3530..cc43bc1 100644
--- a/tests/validation/reference/ActivationLayer.h
+++ b/tests/validation/reference/ActivationLayer.h
@@ -75,6 +75,9 @@
         case ActivationLayerInfo::ActivationFunction::TANH:
             ret = a * std::tanh(b * x);
             break;
+        case ActivationLayerInfo::ActivationFunction::IDENTITY:
+            ret = x;
+            break;
         default:
             ARM_COMPUTE_ERROR("Unsupported activation function");
             break;