kdf: Avoid endianess issues

The key_type is only a letter, if we use and `int` and then cast it to
(const char *) we will end up with a 0 value on big endian.

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>
Reviewed-by: Anderson Toshiyuki Sasaki <ansasaki@redhat.com>

include/libssh/crypto.h

@@ -219,7 +219,7 @@ struct ssh_cipher_struct {
 const struct ssh_cipher_struct *ssh_get_chacha20poly1305_cipher(void);
 int sshkdf_derive_key(struct ssh_crypto_struct *crypto,
                       unsigned char *key, size_t key_len,
-                      int key_type, unsigned char *output,
+                      uint8_t key_type, unsigned char *output,
                       size_t requested_len);
 
 int secure_memcmp(const void *s1, const void *s2, size_t n);