selftests/ftrace: Fix to check the existence of set_ftrace_filter

If we run ftracetest on the kernel with CONFIG_DYNAMIC_FTRACE=n,
there is no set_ftrace_filter and all test cases are failed, because
reset_ftrace_filter() returns an error.
Let's check whether set_ftrace_filter exists in reset_ftrace_filter()
and clean up only set_ftrace_notrace in initialize_ftrace().

Signed-off-by: Masami Hiramatsu <[e-mail]>
Reviewed-by: Steven Rostedt (VMware) <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/ftrace/test.d/functions

···
 }
 
 reset_ftrace_filter() { # reset all triggers in set_ftrace_filter
+    if [ ! -f set_ftrace_filter ]; then
+      return 0
+    fi
     echo > set_ftrace_filter
     grep -v '^#' set_ftrace_filter | while read t; do
 	tr=`echo $t | cut -d: -f2`
···
     disable_events
     [ -f set_event_pid ] && echo > set_event_pid
     [ -f set_ftrace_pid ] && echo > set_ftrace_pid
-    [ -f set_ftrace_filter ] && echo | tee set_ftrace_*
+    [ -f set_ftrace_notrace ] && echo > set_ftrace_notrace
     [ -f set_graph_function ] && echo | tee set_graph_*
     [ -f stack_trace_filter ] && echo > stack_trace_filter
     [ -f kprobe_events ] && echo > kprobe_events