_rtl8821ae_clear_pci_pme_status() accesses the upper byte of the Power
Management Control/Status register (PMCS) with literal 5 offset.

Access the entire PMCS register using defines from pci_regs.h to
improve code readability.

While at it, remove the obvious comment and tweak debug prints
slightly to not sound misleading.
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20231124084725.12738-9-ilpo.jarvinen@linux.intel.com