selftests: ftrace: Use md5sum to take less time of checking logs

Use md5sum so that it takes less time of checking
trace logs update. Since busybox tail/cat takes too
long time to read the trace log, this uses md5sum
to check whether trace log is updated or not.
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/ftrace/test.d/ftrace/func_traceonoff_triggers.tc

@@ -103,11 +103,11 @@ if [ $on != "0" ]; then
     fail "Tracing is not off"
 fi
 
-line1=`cat trace | tail -1`
+csum1=`md5sum trace`
 sleep $SLEEP_TIME
-line2=`cat trace | tail -1`
+csum2=`md5sum trace`
 
-if [ "$line1" != "$line2" ]; then
+if [ "$csum1" != "$csum2" ]; then
     fail "Tracing file is still changing"
 fi