staging: lustre: remove phantom struct cfs_crypto_hash_desc

There is no "struct cfs_crypto_hash_desc" structure.  There
are only pointers to this structure, which are cast back and
forth to struct ahash_request.
So discard cfs_crypto_hash_desc, and just use ahash_request directly.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>