firewire: move fw_device reference counting from drivers to core

fw_unit device drivers invariably need to talk to the fw_unit's parent
(an fw_device) and grandparent (an fw_card).  firewire-core already
maintains an fw_card reference for the entire lifetime of an fw_device.
Likewise, let firewire-core maintain an fw_device reference for the
entire lifetime of an fw_unit so that fw_unit drivers don't have to.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
diff --git a/sound/firewire/isight.c b/sound/firewire/isight.c
index 4400308..412b65f 100644
--- a/sound/firewire/isight.c
+++ b/sound/firewire/isight.c
@@ -612,7 +612,6 @@
 
 	fw_iso_resources_destroy(&isight->resources);
 	fw_unit_put(isight->unit);
-	fw_device_put(isight->device);
 	mutex_destroy(&isight->mutex);
 }
 
@@ -645,7 +644,7 @@
 	isight->card = card;
 	mutex_init(&isight->mutex);
 	isight->unit = fw_unit_get(unit);
-	isight->device = fw_device_get(fw_dev);
+	isight->device = fw_dev;
 	isight->audio_base = get_unit_base(unit);
 	if (!isight->audio_base) {
 		dev_err(&unit->device, "audio unit base not found\n");
@@ -682,7 +681,6 @@
 
 err_unit:
 	fw_unit_put(isight->unit);
-	fw_device_put(isight->device);
 	mutex_destroy(&isight->mutex);
 error:
 	snd_card_free(card);