iommu/omap: Remove unused isr_priv field from omap_iommu

The isr_priv field is a left-over from before the IOMMU API
adaptation, this was used to store the callback data. This is
no longer relevant, so remove it.

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>