PCI/sysfs: Decouple acpi_index from the optional device name element

The "_DSM for Naming a PCI or PCI Express Device Under Operating Systems"
(PCI Firmware r3.3, sec 4.6.7) returns a package of two elements:

  1) Instance number (mandatory Integer)
  2) String name (optional String, null string if not populated)

These are exposed as sysfs 'acpi_index' and 'label'. Previously, if
the name was malformed, reads of 'acpi_index' failed unnecessarily.

Validate each element only for the attribute that exports it.  So
"acpi_index" now depends on the instance number alone, and "label" reads
fail with -EIO when the name element is neither a string nor a buffer.  The
package elements pointer is read only after the object type has been
checked.

On platforms with a valid instance number and a malformed name element the
"acpi_index" attribute starts returning data.  Because udev derives the
onboard interface name from "acpi_index", an interface on such a platform
may be renamed once, on the first boot after this change.  That is the
attribute assuming the value the firmware always provided.

Link: https://github.com/pciutils/pciutils/issues/175
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
[bhelgaas: commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20260814070522.2327975-3-kwilczynski@kernel.org

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