crypto: marvell/cesa - ensure iter.base.op_len is the full op length

When we process the last request of data, and the request contains user
data, the loop in mv_cesa_ahash_dma_req_init() marks the first data size
as being iter.base.op_len which does not include the size of the cache
data.  This means we end up hashing an insufficient amount of data.

Fix this by always including the cache size in the first operation
length of any request.

This has the effect that for a request containing no user data,

	iter.base.op_len === iter.src.op_offset === creq->cache_ptr

As a result, we include one further change to use iter.base.op_len in
the cache-but-no-user-data case to make the next change clearer.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>