PCI: rcar-gen4: Fix -Wvoid-pointer-to-enum-cast error

When building with clang 18 with the -Werror compiler option enabled,
the following error will be reported:

  drivers/pci/controller/dwc/pcie-rcar-gen4.c:439:15: error: cast to smaller integer type 'enum dw_pcie_device_mode' from 'const void *' [-Werror,-Wvoid-pointer-to-enum-cast]
    439 |         rcar->mode = (enum dw_pcie_device_mode)of_device_get_match_data(&rcar->pdev->dev);

To fix this issue, cast the data the of_device_get_match_data() helper
returns to uintptr_t rather than the dw_pcie_device_mode enum.

[kwilczynski: commit log]
Link: https://lore.kernel.org/linux-pci/20231220053829.1921187-7-yoshihiro.shimoda.uh@renesas.com
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>