crypto: omap-sham - fix unaligned sg list handling

Currently the offset for unaligned sg lists is not handled properly
leading into wrong results with certain testmgr self tests. Fix the
handling to account for proper offset within the current sg list.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>