pci: pcie_dw_rockchip: Fixed the below compilation error

pci: pcie_dw_rockchip: Fixed the below compilation error

Use the generic error number instead of specific error number.
Changes fix the below error.

drivers/pci/pcie_dw_rockchip.c: In function 'rk_pcie_read':
drivers/pci/pcie_dw_rockchip.c:70:10: error: 'PCIBIOS_UNSUPPORTED'
                        undeclared (first use in this function)
   70 |   return PCIBIOS_UNSUPPORTED;
      |          ^~~~~~~~~~~~~~~~~~~
drivers/pci/pcie_dw_rockchip.c: In function 'rk_pcie_write':
drivers/pci/pcie_dw_rockchip.c:90:10: error: 'PCIBIOS_UNSUPPORTED'
                        undeclared (first use in this function)
   90 |   return PCIBIOS_UNSUPPORTED;
      |          ^~~~~~~~~~~~~~~~~~~

Cc: Patrick Wildt <patrick@blueri.se>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Patrick Wildt <patrick@blueri.se>
Signed-off-by: Anand Moon <linux.amoon@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>