crypto: inside-secure - refrain from unneeded invalidations

The check to know if an invalidation is needed (i.e. when the context
changes) is done even if the context does not exist yet. This happens
when first setting a key for ciphers and/or hmac operations.

This commits adds a check in the _setkey functions to only check if an
invalidation is needed when a context exists, as there is no need to
perform this check otherwise.

Signed-off-by: Ofer Heifetz <oferh@marvell.com>
[Antoine: commit message and added a comment and reworked one of the
checks]
Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>