selftests/user_events: Enable the event before write_fault test in ftrace self-test

The user_event has not be enabled in write_fault test in ftrace
self-test, Just enable it.

Link: https://lkml.kernel.org/r/20230626111344.19136-3-sunliming@kylinos.cnAcked-by: Beau Belgrave <beaub@linux.microsoft.com>
Signed-off-by: sunliming <sunliming@kylinos.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

tools/testing/selftests/user_events/ftrace_test.c

@@ -400,6 +400,10 @@ TEST_F(user, write_fault) {
 	ASSERT_EQ(0, ioctl(self->data_fd, DIAG_IOCSREG, &reg));
 	ASSERT_EQ(0, reg.write_index);
 
+	/* Enable event */
+	self->enable_fd = open(enable_file, O_RDWR);
+	ASSERT_NE(-1, write(self->enable_fd, "1", sizeof("1")))
+
 	/* Write should work normally */
 	ASSERT_NE(-1, writev(self->data_fd, (const struct iovec *)io, 2));