crypto: cbc - Propagate NEED_FALLBACK bit

When requesting a fallback algorithm, we should propagate the
NEED_FALLBACK bit when search for the underlying algorithm.

This will prevents drivers from allocating unnecessary fallbacks that
are never called. For instance, currently the vmx-crypto driver will use
the following chain of calls when calling the fallback implementation:

p8_aes_cbc -> cbc(p8_aes) -> aes-generic

However p8_aes will always delegate its calls to aes-generic. With this
patch, p8_aes_cbc will be able to use cbc(aes-generic) directly as its
fallback. The same applies to aes_s390.

Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>