smb3: check for null tcon

Although unlikely to be null, it is confusing to use a pointer
before checking for it to be null so move the use down after
null check.

Addresses-Coverity: 1517586 ("Null pointer dereferences  (REVERSE_INULL)")
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/smb2ops.c

@@ -760,8 +760,8 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
 		struct cifs_sb_info *cifs_sb,
 		struct cached_fid **cfid)
 {
-	struct cifs_ses *ses = tcon->ses;
-	struct TCP_Server_Info *server = ses->server;
+	struct cifs_ses *ses;
+	struct TCP_Server_Info *server;
 	struct cifs_open_parms oparms;
 	struct smb2_create_rsp *o_rsp = NULL;
 	struct smb2_query_info_rsp *qi_rsp = NULL;
@@ -780,6 +780,9 @@ int open_cached_dir(unsigned int xid, struct cifs_tcon *tcon,
 	    is_smb1_server(tcon->ses->server))
 		return -ENOTSUPP;
 
+	ses = tcon->ses;
+	server = ses->server;
+
 	if (cifs_sb->root == NULL)
 		return -ENOENT;