iommu/omap: Fix iommu archdata name for DT-based devices

A device is tied to an iommu through its archdata field. The archdata
is allocated on the fly for DT-based devices automatically through the
.add_device iommu ops. The current logic incorrectly assigned the name
of the IOMMU user device, instead of the name of the IOMMU device as
required by the attach logic. Fix this issue so that DT-based devices
can attach successfully to an IOMMU domain.

Signed-off-by: Suman Anna <s-anna@ti.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>