r/elasticache_parameter_group: Add missing return to retry logic

[radeksimko]

This was (unfortunately) forgotten in #1821 🤦‍♂️

which lead to this test failure:

=== RUN   TestAccAWSElasticacheParameterGroup_removeParam
--- FAIL: TestAccAWSElasticacheParameterGroup_removeParam (9.17s)
    testing.go:434: Step 1 error: Error applying: 1 error(s) occurred:
        
        * aws_elasticache_parameter_group.bar: 1 error(s) occurred:
        
        * aws_elasticache_parameter_group.bar: Error resetting Cache Parameter Group: InvalidCacheParameterGroupState: Cannot reset the parameter group because the parameter appendfsync has pending changes.
            status code: 400, request id: fec8c986-afe6-11e7-a315-ef9417804ebe

[Ninir]

Good catch :)

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. Thanks!