iommu/omap: Check for valid archdata in attach_dev

Any device requiring to be attached to an iommu_domain must have
valid archdata containing the necessary iommu information, which
is SoC-specific. Add a check in the omap_iommu_attach_dev to make
sure that the device has valid archdata before accessing
different SoC-specific fields of the archdata. This prevents a
NULL pointer dereference on any misconfigured devices.

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>