[media] Revert "[media] sound/usb: Use Media Controller API to share media resources"

Unfortunately, this patch caused several regressions at au0828 and
snd-usb-audio, like this one:
	https://bugzilla.kernel.org/show_bug.cgi?id=115561

It also showed several troubles at the MC core that handles pretty
poorly the memory protections and data lifetime management.

So, better to revert it and fix the core before reapplying this
change.

This reverts commit aebb2b89bf ("[media] sound/usb: Use Media
Controller API to share media resources")'

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

sound/usb/mixer.h

@@ -3,8 +3,6 @@
 
 #include <sound/info.h>
 
-struct media_mixer_ctl;
-
 struct usb_mixer_interface {
 	struct snd_usb_audio *chip;
 	struct usb_host_interface *hostif;
@@ -24,7 +22,6 @@ struct usb_mixer_interface {
 	struct urb *rc_urb;
 	struct usb_ctrlrequest *rc_setup_packet;
 	u8 rc_buffer[6];
-	struct media_mixer_ctl *media_mixer_ctl;
 };
 
 #define MAX_CHANNELS	16	/* max logical channels */