Return -EINVAL if a request for a block cipher is not multiple of the
size of the block.

This problem was found with by the new extra run-time crypto self test.
Reviewed-by: Conor Mcloughlin <conor.mcloughlin@intel.com>
Tested-by: Sergey Portnoy <sergey.portnoy@intel.com>
Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>