usb: simplify usbport trigger

The led trigger core learned a few things that allow to simplify the
trigger drivers.  Make use of automated trigger attributes and error
checking of the activate callback. Also use the wrappers to set and get
trigger_data.

Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>