- remove the unnecessary map_single path.
- convert to use the new accessors for the sg lists and the parameters.

Fixed to missing initialization of sg lists before calling
for_each_sg() by Jes Sorensen - sg list needs to be initialized before
trying to pull the elements out of it.
Signed-off-by: NFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: NJes Sorensen <jes@sgi.com>
Signed-off-by: NJames Bottomley <James.Bottomley@HansenPartnership.com>