dma-mapping: don't return errors from dma_set_seg_boundary

A NULL dev->dma_parms indicates either a bus that is not DMA capable or
grave bug in the implementation of the bus code.

There isn't much the driver can do in terms of error handling for either
case, so just warn and continue as DMA operations will fail anyway.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>