_krb5_mk_req_internal() accepts a (krb5_auth_context *) because
it can allocate and return a krb5_auth_context to the caller.
mkae_pa_tgs_req() should never be called with a non-NULL
krb5_auth_context but to avoid confusion, alter the signature
to accept a (krb5_auth_context *) instead of (krb5_auth_context)
so _krb5_mk_req_internal() is not called with a pointer to an
input parameter.
Change-Id: I6c2293529766eb06a9eebf41715533d8195b1f72
0a088b9b61