iommu/omap: Simplify omap2_iommu_fault_isr()

The function omap2_iommu_fault_isr() does an unnecessary
recomputation of the return value. The logic relies on
setting the same bit fields as the MMU fault error status
bits, so simplify this function and remove the unneeded
macros. These macros were originally exported to notify
MMU faults to users prior to the IOMMU framework adaptation,
but are now redundant.

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>