PCI/portdrv: Drop empty shutdown callback

PCI/portdrv: Drop empty shutdown callback

.shutdown() is an optional callback and the core only calls it if the
pointer in struct device_driver is non-NULL. So make nothing in a bit
shorter time and remove the empty function.

Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://patch.msgid.link/283fef06ac51efbb7df25f347d6f3a2967f96429.1764688034.git.u.kleine-koenig@baylibre.com