tracing/selftests: Fix kprobe event name test for .isra. functions

The kprobe_eventname.tc test checks if a function with .isra. can have a
kprobe attached to it. It loops through the kallsyms file for all the
functions that have the .isra. name, and checks if it exists in the
available_filter_functions file, and if it does, it uses it to attach a
kprobe to it.

The issue is that kprobes can not attach to functions that are listed more
than once in available_filter_functions. With the latest kernel, the
function that is found is: rapl_event_update.isra.0

# grep rapl_event_update.isra.0 /sys/kernel/tracing/available_filter_functions
rapl_event_update.isra.0
rapl_event_update.isra.0

It is listed twice. This causes the attached kprobe to it to fail which in
turn fails the test. Instead of just picking the function function that is
found in available_filter_functions, pick the first one that is listed
only once in available_filter_functions.

Cc: [e-mail]
Fixes: 604e3548236d ("selftests/ftrace: Select an existing function in kprobe_eventname test")
Signed-off-by: Steven Rostedt (Google) <[e-mail]>
Acked-by: Masami Hiramatsu (Google) <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/ftrace/test.d/kprobe/kprobe_eventname.tc

···
 	fi
 
 	grep " [tT] .*\.isra\..*" /proc/kallsyms | cut -f 3 -d " " | while read f; do
-		if grep -s $f available_filter_functions; then
+		cnt=`grep -s $f available_filter_functions | wc -l`;
+		if [ $cnt -eq 1 ]; then
 			echo $f
 			break
 		fi