The .map_sg() op now expects an error code instead of zero on failure.

pci_map_single_1() can fail for different reasons, but since the only
supported type of error return is DMA_MAPPING_ERROR, we coalesce those
errors into EIO.

ENOMEM is returned when no page tables can be allocated.
Signed-off-by: Martin Oliveira <martin.oliveira@eideticom.com>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>