PCI: Update saved Max Payload Size in pcie_set_mps()

pcie_set_mps() changes the Max Payload Size (MPS) in the Device Control
register but leaves the copy saved by pci_save_state() alone, so the next
pci_restore_state() puts back the old value.

The PCI core does change the MPS of devices whose state has already been
saved: pci_configure_mps() reduces a Root Port's MPS when a device with a
smaller MPS Supported is hot-added directly below it (commit 9f0e89359775
("PCI: Match Root Port's MPS to endpoint's MPSS as necessary")), and with
"pci=pcie_bus_safe", pcie_bus_configure_settings() can do the same when
pciehp calls it after a hot-add.  The Root Port's state was saved when it
was added and again when portdrv probed it.

Since commit 3fc686d550f6 ("PCI/ERR: Add support for resetting the Root
Ports in a platform-specific way"), pcibios_reset_secondary_bus() restores
that saved state, without saving it first, after host->reset_root_port()
has reset the Root Port, e.g. during AER recovery or on Link Down with the
qcom and Rockchip DWC drivers.  The Root Port then goes back to the old,
larger MPS while the device below it is restored to the smaller one, so the
Root Port may send TLPs that the device treats as Malformed.

Update the saved copy of Device Control when pcie_set_mps() changes the
MPS, like commit 909f7bf9b080 ("PCI: Update saved_config_space upon
resource assignment") does for BARs.

Fixes: 3fc686d550f6 ("PCI/ERR: Add support for resetting the Root Ports in a platform-specific way")
Assisted-by: LLM
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Link: https://patch.msgid.link/20261005124154.2190628-2-cassel@kernel.org

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