crypto: sahara - fix processing requests with cryptlen < sg->length

crypto: sahara - fix processing requests with cryptlen < sg->length

It's not always the case that the entire sg entry needs to be processed.
Currently, when cryptlen is less than sg->legth, "Descriptor length" errors
are encountered.

The error was noticed when testing xts(sahara-ecb-aes) with arbitrary sized
input data. To fix this, take the actual request size into account when
populating the hw links.

Fixes: 5de8875281e1 ("crypto: sahara - Add driver for SAHARA2 accelerator.")
Signed-off-by: Ovidiu Panait <ovidiu.panait@windriver.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>