Remove reference to pci_p2pmem_dma(), which has never existed.

Link: https://lore.kernel.org/r/20230329024731.5604-1-cai.huoqing@linux.devSigned-off-by: Cai Huoqing <cai.huoqing@linux.dev>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>