parisc: return error code from .map_sg() ops

The .map_sg() op now expects an error code instead of zero on failure.
Return -EINVAL if the ioc cannot be obtained.

Signed-off-by: Martin Oliveira <martin.oliveira@eideticom.com>
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Helge Deller <deller@gmx.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>