remove the ->mapping_error method from dma_map_ops V2

On Fri, Nov 23, 2018 at 07:55:11AM +0100, Christoph Hellwig wrote:

On Thu, Nov 22, 2018 at 09:55:25AM -0800, Linus Torvalds wrote:

quoted

No, the big immediate benefit of allowing "return -EINVAL" etc is
simply legibility and error avoidance.

Well, I can tweak the last patch to return -EINVAL from dma_mapping_error
instead of the old 1 is as bool true.  The callers should all be fine,
although I'd have to audit them.  Still wouldn't help with being able to
return different errors.

Any opinions?  I'd really like to make some forward progress on this
series.