read_fd_link(): don't overrun buf

This is a classical off-by-one error. If sizeof(buf) is 512,
the last element is buf[511] but not buf[512].

Reported by Coverity, CID 114624, 114622 etc.
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

util.c

@@ -467,7 +467,7 @@ int read_fd_link(int lfd, char *buf, size_t size)
 		pr_err("Buffer for read link of fd %d is too small\n", lfd);
 		return -1;
 	}
-	buf[ret] = 0;
+	buf[ret - 1] = 0;
 
 	return ret;
 }