greybus: interface: fix interface_id attribute group

All interfaces, regardless of type, should have an interface_id
attribute reflecting its position on the frame.

This has been reported to cause an assertion failure in libmoduleutil
for dummy modules.

Testing done: Verified that the attribute is present for registered
dummy interfaces.
Reported-by: Gjorgji Rosikopulos <grosikopulos@mm-sol.com>
Tested-by: Gjorgji Rosikopulos <grosikopulos@mm-sol.com>
Reviewed-by: Patrick Titiano <ptitiano@baylibre.com>
Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/interface.c

@@ -587,7 +587,6 @@ static struct attribute *interface_unipro_attrs[] = {
 };
 
 static struct attribute *interface_greybus_attrs[] = {
-	&dev_attr_interface_id.attr,
 	&dev_attr_vendor_id.attr,
 	&dev_attr_product_id.attr,
 	&dev_attr_serial_number.attr,
@@ -603,6 +602,7 @@ static struct attribute *interface_power_attrs[] = {
 };
 
 static struct attribute *interface_common_attrs[] = {
+	&dev_attr_interface_id.attr,
 	&dev_attr_interface_type.attr,
 	NULL
 };