Use device_delete_children instead of explicit calls to device_delete_child

This is simpler and more robust in the face of potential double-frees
(e.g. if called after bus_generic_detach which will delete devices in
a future commit).

Reviewed by:	manu, imp
Differential Revision:	https://reviews.freebsd.org/D47958

sys/arm/allwinner/aw_mmc.c

@@ -482,7 +482,6 @@ static int
 aw_mmc_detach(device_t dev)
 {
 	struct aw_mmc_softc *sc;
-	device_t d;
 
 	sc = device_get_softc(dev);
 
@@ -494,12 +493,7 @@ aw_mmc_detach(device_t dev)
 
 	callout_drain(&sc->aw_timeoutc);
 
-	AW_MMC_LOCK(sc);
-	d = sc->child;
-	sc->child = NULL;
-	AW_MMC_UNLOCK(sc);
-	if (d != NULL)
-		device_delete_child(sc->aw_dev, d);
+	device_delete_children(sc->aw_dev);
 
 	aw_mmc_teardown_dma(sc);
 

sys/arm64/broadcom/genet/if_genet.c

@@ -365,10 +365,7 @@ static void
 gen_destroy(struct gen_softc *sc)
 {
 
-	if (sc->miibus) {	/* can't happen */
-		device_delete_child(sc->dev, sc->miibus);
-		sc->miibus = NULL;
-	}
+	device_delete_children(sc->dev);
 	bus_teardown_intr(sc->dev, sc->res[_RES_IRQ1], sc->ih);
 	bus_teardown_intr(sc->dev, sc->res[_RES_IRQ2], sc->ih2);
 	gen_bus_dma_teardown(sc);

sys/dev/intpm/intpm.c

@@ -202,8 +202,7 @@ intsmb_release_resources(device_t dev)
 {
 	struct intsmb_softc *sc = device_get_softc(dev);
 
-	if (sc->smbus)
-		device_delete_child(dev, sc->smbus);
+	device_delete_children(dev);
 	if (sc->irq_hand)
 		bus_teardown_intr(dev, sc->irq_res, sc->irq_hand);
 	if (sc->irq_res)