[LTP] [PATCH] Fix disable set_ftrace_pid in ftrace_set_ftrace_pid.sh

[Han P. <ph...@re...>]

It seems we need echo -1 to set_ftrace_pid to disable in. Or we'll get
these error message when running ftrace_stress:

...
ftrace_stress_test/ftrace_stress/ftrace_set_ftrace_pid.sh: line 39: echo: write error: Invalid argument
...
---
 .../ftrace_stress/ftrace_set_ftrace_pid.sh         |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/testcases/kernel/tracing/ftrace_stress_test/ftrace_stress/ftrace_set_ftrace_pid.sh b/testcases/kernel/tracing/ftrace_stress_test/ftrace_stress/ftrace_set_ftrace_pid.sh
index 541215c..bd08f04 100755
--- a/testcases/kernel/tracing/ftrace_stress_test/ftrace_stress/ftrace_set_ftrace_pid.sh
+++ b/testcases/kernel/tracing/ftrace_stress_test/ftrace_stress/ftrace_set_ftrace_pid.sh
@@ -36,7 +36,7 @@ for ((; ; ))
 			eval echo $str >> "$TRACING_PATH"/set_ftrace_pid
 		}
 
-		echo > "$TRACING_PATH"/set_ftrace_pid
+		echo -1 > "$TRACING_PATH"/set_ftrace_pid
 	}
 
 	sleep 1
-- 
1.7.1