iommu/omap: Add check for iommu group when no IOMMU in use

iommu/omap: Add check for iommu group when no IOMMU in use

Most of the devices in OMAP family of SoCs are not using IOMMU. The
patch for converting the OMAP IOMMU to use generic IOMMU bus probe
functionality failed to add a check for this, so add it here.

Fixes: c822b37cac48 ("iommu/omap: Remove orphan_dev tracking")
Reported-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Link: https://lore.kernel.org/r/20200518111057.23140-1-t-kristo@ti.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>