[aws-for-fluent-bit] Log Group retention time setting not working.

**Describe the bug**
The option "cloudWatch.logRetentionDays" doesn't set the log retention days setting of the resulting CloudWatch log group.

**Steps to reproduce**

```
cloudWatch:
region: us-east-1
logGroupName: /aws/eks/blah/fluentbit-cloudwatch
logRetentionDays: 3
logKey: log
firehose:
enabled: false
kinesis:
enabled: false
elasticsearch:
enabled: false
```

**Expected outcome**
The resulting log group should have a retention policy of 3 days. However it is set with a "Never expire" retention policy.

**Environment**

* Chart name: aws-for-fluent-bit
* Chart version: 0.1.5
* Kubernetes version: EKS 1.18