Workaround to allow weight = 0 in Route53 RRs

Moved the GetOk to a Get in the set_identifier block so
we can create a zero-weighted RR - otherwise this falls foul
of a check in GetOk.

See https://github.com/hashicorp/terraform/issues/3189

builtin/providers/aws/resource_aws_route53_record.go

@@ -407,12 +407,9 @@ func resourceAwsRoute53RecordBuildSet(d *schema.ResourceData, zoneName string) (
 		rec.HealthCheckId = aws.String(v.(string))
 	}
 
-	if v, ok := d.GetOk("weight"); ok {
-		rec.Weight = aws.Int64(int64(v.(int)))
-	}
-
 	if v, ok := d.GetOk("set_identifier"); ok {
 		rec.SetIdentifier = aws.String(v.(string))
+		rec.Weight = aws.Int64(int64(d.Get("weight").(int)))
 	}
 
 	return rec, nil