PCI: cleanup assign_requested_resources_sorted() kernel-doc warning

Warning(drivers/pci/setup-bus.c:277): No description found for parameter 'fail_head'
Warning(drivers/pci/setup-bus.c:277): Excess function parameter 'failed_list' description in 'assign_requested_resources_sorted'

Signed-off-by: Wanpeng Li <liwp.linux@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>