PCI: rockchip: Remove writes to unused registers

Remove write accesses to registers that are marked "unused" (and
therefore read-only) in the technical reference manual (TRM)
(see RK3399 TRM 17.6.8.1)

Link: https://lore.kernel.org/r/20230418074700.1083505-2-rick.wertenbroek@gmail.com


Tested-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Rick Wertenbroek <rick.wertenbroek@gmail.com>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>