s390/pci: return error code from s390_dma_map_sg()

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

So propagate the error from __s390_dma_map_sg() up. __s390_dma_map_sg()
returns either -ENOMEM on allocation failure or -EINVAL which is
the same as what's expected by dma_map_sgtable().

Signed-off-by: Martin Oliveira <martin.oliveira@eideticom.com>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Niklas Schnelle <schnelle@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>