counter: stm32-lptimer-cnt: Convert to new counter registration

counter: stm32-lptimer-cnt: Convert to new counter registration

This fixes device lifetime issues where it was possible to free a live
struct device.

Fixes: 597f55e3f36c ("counter: stm32-lptimer: add counter device")
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20211230150300.72196-22-u.kleine-koenig@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>