uni-t-ut32x: pre-set to default conn= spec

The previous implementation of the UT32x driver expected to see a conn=
spec, without it no device is found. Default to the USB identification
of the CH9325 chip, to make the driver work out of the box. Users still
can provide conn= specs and override the default for other cables.

src/hardware/uni-t-ut32x/api.c

@@ -55,7 +55,7 @@ static GSList *scan(struct sr_dev_driver *di, GSList *options)
 
 	drvc = di->context;
 
-	conn = NULL;
+	conn = "1a86.e008";
 	for (l = options; l; l = l->next) {
 		src = l->data;
 		switch (src->key) {