tca6416: add support for tca9539

Programming-wise tca6416 and tca9539 seem identical so all we have to
do is add the extra ofw_compat_data line.

MFC after:	2 weeks
Reviewed by:	mw
Differential Revision: https://reviews.freebsd.org/D35702

sys/dev/iicbus/gpio/tca6416.c

@@ -136,6 +136,7 @@ MODULE_VERSION(tca6416, 1);
 
 static struct ofw_compat_data compat_data[] = {
 	{"ti,tca6416",	1},
+	{"ti,tca9539",	1},
 	{0,0}
 };