VT-d/ATS: cleanup

VT-d/ATS: cleanup

- make acpi_find_matched_atsr_unit() consistent with
  acpi_find_matched_drhd_unit() (and constify their parameter)
- make ats_device() take a struct pci_dev * instead of seg:bus:devfn
  and additionally the matching DRHD (as its callers already worked
  that out)
- remove a stale prototype

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: "Kay, Allen M" <allen.m.kay@intel.com>