eCryptfs: Fix payload_len unitialized variable warning

fs/ecryptfs/keystore.c: In function ‘ecryptfs_generate_key_packet_set’:
fs/ecryptfs/keystore.c:1991:28: warning: ‘payload_len’ may be used uninitialized in this function [-Wuninitialized]
fs/ecryptfs/keystore.c:1976:9: note: ‘payload_len’ was declared here

Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>

fs/ecryptfs/keystore.c

@@ -1973,7 +1973,7 @@ pki_encrypt_session_key(struct key *auth_tok_key,
 {
 	struct ecryptfs_msg_ctx *msg_ctx = NULL;
 	char *payload = NULL;
-	size_t payload_len;
+	size_t payload_len = 0;
 	struct ecryptfs_message *msg;
 	int rc;