PCI: dwc: ep: Fix MSI-X Table Size configuration in dw_pcie_ep_set_msix()

PCI: dwc: ep: Fix MSI-X Table Size configuration in dw_pcie_ep_set_msix()

In dw_pcie_ep_set_msix(), while updating the MSI-X Table Size value for
individual functions, Message Control register is read from the passed
function number register space using dw_pcie_ep_readw_dbi(), but always
written back to the Function 0's register space using dw_pcie_writew_dbi().
This causes incorrect MSI-X configuration for the rest of the functions,
other than Function 0.

Fix this by using dw_pcie_ep_writew_dbi() to write to the correct
function's register space, matching the read operation.

Fixes: 70fa02ca1446 ("PCI: dwc: Add dw_pcie_ep_{read,write}_dbi[2] helpers")
Signed-off-by: Aksh Garg <a-garg7@ti.com>
[mani: commit log]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Link: https://patch.msgid.link/20260224083817.916782-2-a-garg7@ti.com