Fix leak in k5_free_cammac()

free_vmac(), a helper function used by k5_free_cammac(), must free its
val pointer as well as the contents; otherwise the krb5_verifier_mac
container is leaked.

(cherry picked from commit d9d6e7e9aa619d5bd35fa6e4468683ee7ddb5e5d)

https://github.com/krb5/krb5/commit/1590b0e06e0daae413fbf72effcd8335ec05b618
Author: Greg Hudson <ghudson@mit.edu>
Committer: Tom Yu <tlyu@mit.edu>
Commit: 1590b0e06e0daae413fbf72effcd8335ec05b618
Branch: krb5-1.14
 src/lib/krb5/krb/kfree.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)