gpio: Fix incorrect dev being passed to gpiobus_detach_bus

Passing in the busdev will not detach from the bus correctly leaving the
/dev/gpiocN entry

Reviewed by:	vexeduxr, imp
Differential Revision:	https://reviews.freebsd.org/D51857

Author: Evgenii Ivanov

sys/dev/iicbus/gpio/pcf8574.c

@@ -159,9 +159,7 @@ pcf8574_detach(device_t dev)
 
 	sc = device_get_softc(dev);
 
-	if (sc->busdev != NULL)
-		gpiobus_detach_bus(sc->busdev);
-
+	gpiobus_detach_bus(dev);
 	sx_destroy(&sc->lock);
 	return (0);
 }

sys/dev/iicbus/gpio/tca64xx.c

@@ -292,9 +292,7 @@ tca64xx_detach(device_t dev)
 
 	sc = device_get_softc(dev);
 
-	if (sc->busdev != NULL)
-		gpiobus_detach_bus(sc->busdev);
-
+	gpiobus_detach_bus(dev);
 	mtx_destroy(&sc->mtx);
 
 	return (0);