Setting the ->dma_address to DMA_MAPPING_ERROR is not part of
the ->map_sg calling convention, so remove it.

Link: https://lore.kernel.org/linux-mips/20210716063241.GC13345@lst.de/Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Niklas Schnelle <schnelle@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Christoph Hellwig <hch@lst.de>