eCryptfs: initialize payload_len in keystore.c

This is meant to remove a compiler warning.  It should not make any
functional change.

payload_len should be initialized when it is passed to
write_tag_64_packet() as a pointer.  If that call fails, this function
should return early, and payload_len won't be used.
Signed-off-by: Simon Que <sque@chromium.org>
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>

fs/ecryptfs/keystore.c

@@ -1150,7 +1150,7 @@ decrypt_pki_encrypted_session_key(struct ecryptfs_auth_tok *auth_tok,
 	struct ecryptfs_message *msg = NULL;
 	char *auth_tok_sig;
 	char *payload;
-	size_t payload_len;
+	size_t payload_len = 0;
 	int rc;
 
 	rc = ecryptfs_get_auth_tok_sig(&auth_tok_sig, auth_tok);