cpulog: set line buffering

Otherwise it collects a bunch of measurements and outputs them
all at once.

Change-Id: I366fad04464fac127d428587228bf928cdd9a5fb
diff --git a/cmds/cpulog.c b/cmds/cpulog.c
index ff8498a..f58b17b 100644
--- a/cmds/cpulog.c
+++ b/cmds/cpulog.c
@@ -229,6 +229,8 @@
   if (optind < argc)
     usage_and_die(argv[0]);
 
+  setlinebuf(stdout);
+
   ticks_per_sec = sysconf(_SC_CLK_TCK);
 
   sleep(warmup_seconds);