PCI/MSI: Fix msi_capability_init() kernel-doc warnings

Fix kernel-doc warnings in pci/msi.c:

  ..//drivers/pci/msi.c:623: warning: No description found for parameter 'affd'
  ..//drivers/pci/msi.c:623: warning: Excess function parameter 'affinity' description in 'msi_capability_init'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>