[CRYPTO] api: Do not remove users unless new algorithm matches

As it is whenever a new algorithm with the same name is registered
users of the old algorithm will be removed so that they can take
advantage of the new algorithm.  This presents a problem when the
new algorithm is not equivalent to the old algorithm.  In particular,
the new algorithm might only function on top of the existing one.

Hence we should not remove users unless they can make use of the
new algorithm.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>