Do not use DMA is the request is 0 length.
Signed-off-by: NAntoine Tenart <antoine.tenart@free-electrons.com>
Tested-by: NCorentin Labbe <clabbe.montjoie@gmail.com>
Acked-by: NCorentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>