IOMMU: allow MSI message to IRTE propagation to fail

IOMMU: allow MSI message to IRTE propagation to fail

With the need to allocate multiple contiguous IRTEs for multi-vector
MSI, the chance of failure here increases. While on the AMD side
there's no allocation of IRTEs at present at all (and hence no way for
this allocation to fail, which is going to change with a later patch in
this series), VT-d already ignores an eventual error here, which this
patch fixes.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: "Zhang, Xiantao" <xiantao.zhang@intel.com>