PCI/P2PDMA: Cleanup __pci_p2pdma_map_sg a bit

Remove the pointless paddr variable that was only used once.

Link: https://lore.kernel.org/r/20201106181941.1878556-10-hch@lst.de


Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>