PCI: Fix 32-bit config write in Intel PCH Root Port MPC ACS quirk

pci_quirk_enable_intel_rp_mpc_acs() reads a 32-bit DWORD from the MPC
register, sets bit 26 (INTEL_MPC_REG_IRBNCE), but it writes it back using
pci_write_config_word().

Because bit 26 resides in the upper 16 bits of the 32-bit register, a
16-bit write drops the newly set bit. The quirk logs that it is enabling
IRBNCE, but the hardware never actually receives the command.

Use pci_write_config_dword() to ensure the full 32-bit value is written
back to the hardware.

Fixes: d99321b63b1f ("PCI: Enable quirks for PCIe ACS on Intel PCH root ports")
Signed-off-by: Mohamad Raizudeen <raizudeen.kerneldev@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260723171203.4892-1-raizudeen.kerneldev@gmail.com

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