sparc64: Fix memory leak in pci_register_iommu_region().

Found by kmemleak.

If request_resource() fails, we leak the struct resource we
allocated to represent the IOMMU mapping area.

This actually happens on sun4v machines because the IOMEM area is only
reported sans the IOMMU region, unlike all previous systems.  I'll
need to fix that at some point, but for now fix the leak.

Signed-off-by: David S. Miller <davem@davemloft.net>