PCI/doc: Update obsolete pci_set_dma_mask() references

The function is dma_set_mask(), fix a missed instance of the old
pci_set_dma_mask() and a reference to a function that doesn't exist.

Fixes: 05b0ebd0 ("PCI/doc: cleanup references to the legacy PCI DMA API")
Link: https://lore.kernel.org/r/165048747271.2959320.13475081883467312497.stgit@omen


Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>