thanks to luk2302 for pointing out the issue, ec2:CreateTags was missing in my policy statement below is my updated policy

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "ec2:CreateSnapshot",
                "ec2:DescribeInstances",
                "ec2:DescribeVolumes"
            ],
            "Resource": "*"
        },
        {
            "Effect": "Allow",
            "Action": [
                "ec2:CreateTags"
            ],
            "Resource": "*"
        }
    ]
}

below document is helpful too.. https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/supported-iam-actions-tagging.html