PCI/P2PDMA: Apply bus offset correctly in DMA address calculation

The bus offset is bus address - physical address, so the calculation in
__pci_p2pdma_map_sg should be: bus address = physical address + bus offset.

Correct the dma_address computation in __pci_p2pdma_map_sg().

Link: https://lore.kernel.org/r/20210909032528.24517-1-wanglu@dapustor.comSigned-off-by: Wang Lu <wanglu@dapustor.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>

drivers/pci/p2pdma.c

@@ -874,7 +874,7 @@ static int __pci_p2pdma_map_sg(struct pci_p2pdma_pagemap *p2p_pgmap,
 	int i;
 
 	for_each_sg(sg, s, nents, i) {
-		s->dma_address = sg_phys(s) - p2p_pgmap->bus_offset;
+		s->dma_address = sg_phys(s) + p2p_pgmap->bus_offset;
 		sg_dma_len(s) = s->length;
 	}