[CPU] Added improvements for Mish (#5062)

inference-engine/tests/functional/shared_test_classes/src/single_layer/activation.cpp

@@ -95,6 +95,12 @@ InferenceEngine::Blob::Ptr ActivationLayerTest::GenerateInput(const InferenceEng
             resolution = 4;
             break;
         }
+        case ngraph::helpers::ActivationTypes::Mish: {
+            data_start_from = -20;
+            data_range = 60;
+            resolution = 32768;
+            break;
+        }
         default: {
             data_start_from = -10;
             data_range = 20;