pci: ensure valid link status bits for downstream ports

pci: ensure valid link status bits for downstream ports

PCI hotplug for downstream endpoints on arm fails because Linux'
PCIe hotplug driver doesn't like the QEMU provided LNKSTA:

  pcieport 0000:08:01.0: pciehp: Slot(2): Card present
  pcieport 0000:08:01.0: pciehp: Slot(2): Link Up
  pcieport 0000:08:01.0: pciehp: Slot(2): Cannot train link: status 0x2000

There's 2 cases where LNKSTA isn't setup properly:
* the downstream device has no express capability
* max link width of the bridge is 0

Move the sanity checks added via 88c869198aa63
("pci: Sanity test minimum downstream LNKSTA") outside of the
branch to make sure downstream ports always have a valid LNKSTA.

Signed-off-by: Sebastian Ott <sebott@redhat.com>
Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>
Message-Id: <20241203121928.14861-1-sebott@redhat.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit 694632fd44987cc4618612a38ad151047524a590)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>