Allow diff of iops when volume_type is io1
Allow diff of iops when volume_type is io1

Iops can only be specified with io1. Only perform the diff when the
volume_type is io1.

Ninir/terraform-provider-aws,nbaztec/terraform-provider-aws,Ninir/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,ClementCunin/terraform-provider-aws,ClementCunin/terraform-provider-aws,nbaztec/terraform-provider-aws,nbaztec/terraform-provider-aws,ClementCunin/terraform-provider-aws,Ninir/terraform-provider-aws,terraform-providers/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,nbaztec/terraform-provider-aws,terraform-providers/terraform-provider-aws,Ninir/terraform-provider-aws,ClementCunin/terraform-provider-aws,kjmkznr/terraform-provider-aws,kjmkznr/terraform-provider-aws,terraform-providers/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,kjmkznr/terraform-provider-aws