selftests/ftrace: Fix BTFARG testcase to check fprobe is enabled correctly

Since the dynevent/add_remove_btfarg.tc test case forgets to ensure that
fprobe is enabled for some structure field access tests which uses the
fprobe, it fails if CONFIG_FPROBE=n or CONFIG_FPROBE_EVENTS=n.
Fixes it to ensure the fprobe events are supported.

Fixes: d892d3d3 ("selftests/ftrace: Add BTF fields access testcases")
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/ftrace/test.d/dynevent/add_remove_btfarg.tc

@@ -53,7 +53,7 @@ fi
 
 echo > dynamic_events
 
-if [ "$FIELDS" ] ; then
+if [ "$FIELDS" -a "$FPROBES" ] ; then
 echo "t:tpevent ${TP2} obj_size=s->object_size" >> dynamic_events
 echo "f:fpevent ${TP3}%return path=\$retval->name:string" >> dynamic_events
 echo "t:tpevent2 ${TP4} p->se.group_node.next->prev" >> dynamic_events