PCI: Don't treat ~0 as ready in pci_dev_wait() with RRS SV

With RRS Software Visibility, pci_dev_wait() considers a device ready as
soon as reading the Vendor ID doesn't return the RRS value.  Devices aren't
required to respond with RRS while they aren't ready, so the read may
return ~0 and pci_dev_wait() stops waiting too early.  This was seen with
Intel [8086:0a54] and Samsung [144d:a80c] NVMe SSDs.

Also wait while the Vendor ID reads ~0.  A VF's Vendor ID always reads ~0,
so check its Command register instead, as is done without RRS SV.

Fixes: d591f6804e7e ("PCI: Wait for device readiness with Configuration RRS")
Link: https://lore.kernel.org/r/20250611101442.387378-1-hui.wang@canonical.com
Suggested-by: Lukas Wunner <lukas@wunner.de>
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Alexander Gruhlke <gruhlke@mailbox.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Link: https://patch.msgid.link/20261011190145.23621-3-gruhlke@mailbox.org

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