A few fixes in the EVP_KDF-KB and EVP_KDF-KRB5KDF manpages

The context and label is info and salt respectively - fix
the example in KB manpage for that.

There are some typos and bug in EVP_KDF_derive call in the
KRB5KDF example.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/10426)
