iommu: Fix loss of errno on map failure for classic ops
A typo, likely from a rebase, inverted the condition and caused
errors to be lost. Fix it to be "if (ret)".
This was breaking iommu_create_device_direct_mappings() on drivers
that don't use iommupt and don't fully set up their domain in
alloc_pages() (i.e., SMMUv2). In this case the first call of
iommu_create_device_direct_mappings() should fail due to the
incompletely initialized domain. Since it wrongly returns success,
the second call to iommu_create_device_direct_mappings() doesn't
happen and IOMMU_RESV_DIRECT is never set up.