iommu: Simplify and fix ida handling

Ida handling can be much simplified by using the ida_simple_.. functions.

This change also fixes the bug that previously checking for errors
returned by ida_get_new() was incomplete.
ida_get_new() can return errors other than EAGAIN, e.g. ENOSPC.
This case wasn't handled.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>