ACPI: bus: Drop driver member of struct acpi_device

struct acpi_device::driver tracks the same information as the driver
member of struct acpi_device::dev.

Fix all users of the former to use the latter and drop the redundant
data from struct acpi_device.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>