prevent unused variable error (aws-controllers-k8s#101)

A [previous commit][0] that changed the ACK pkg/resource templates
introduced an error for controllers that have CREATE or UPDATE
implementations where the Output shape from the operation sets no fields
on the CR.

In these cases, attempting to build these controllers was resulting in a
build failure, like this for the RDS controller:

```
pkg/resource/db_parameter_group/sdk.go:205:6: resp declared but not used
```

This corrects that by using a blanking technique immediately after the
variable declaration:

```
var resp *SomeSDKShape; _ = resp;
```

[0]: a42b4a1

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Author: jaypipes

templates/pkg/resource/sdk.go.tpl

@@ -70,7 +70,7 @@ func (rm *resourceManager) sdkCreate(
 {{ $hookCode }} 
 {{- end }}
 
-	var resp {{ .CRD.GetOutputShapeGoType .CRD.Ops.Create }}
+	var resp {{ .CRD.GetOutputShapeGoType .CRD.Ops.Create }}; _ = resp;
 	resp, err = rm.sdkapi.{{ .CRD.Ops.Create.ExportedName }}WithContext(ctx, input)
 {{- if $hookCode := Hook .CRD "sdk_create_post_request" }}
 {{ $hookCode }}

templates/pkg/resource/sdk_update.go.tpl

@@ -26,7 +26,7 @@ func (rm *resourceManager) sdkUpdate(
 {{ $hookCode }} 
 {{- end }}
 
-	var resp {{ .CRD.GetOutputShapeGoType .CRD.Ops.Update }}
+	var resp {{ .CRD.GetOutputShapeGoType .CRD.Ops.Update }}; _ = resp;
 	resp, err = rm.sdkapi.{{ .CRD.Ops.Update.ExportedName }}WithContext(ctx, input)
 {{- if $hookCode := Hook .CRD "sdk_update_post_request" }}
 {{ $hookCode }}