[PATCH] uapi: fix linux/usb/audio.h userspace compilation error

[Dmitry V. Levin]

Replace NULL with 0 in uac_mixer_unit_bmControls() to fix the following
linux/usb/audio.h userspace compilation error:

/usr/include/linux/usb/audio.h: In function 'uac_mixer_unit_bmControls':
/usr/include/linux/usb/audio.h:304:10: error: 'NULL' undeclared (first use in this function)
   return NULL;

Fixes: 6cfd839ae78e ("ALSA: usb-audio: UAC3. Add support for mixer unit.")
Cc: <stable@xxxxxxxxxxxxxxx> # v4.18
Signed-off-by: Dmitry V. Levin <ldv@xxxxxxxxxxxx>
---
 include/uapi/linux/usb/audio.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/uapi/linux/usb/audio.h b/include/uapi/linux/usb/audio.h
index 74e520fb944f..2b61fe34b2ca 100644
--- a/include/uapi/linux/usb/audio.h
+++ b/include/uapi/linux/usb/audio.h
@@ -301,7 +301,7 @@ static inline __u8 *uac_mixer_unit_bmControls(struct uac_mixer_unit_descriptor *
 	case UAC_VERSION_3:
 		return &desc->baSourceID[desc->bNrInPins + 2];
 	default:
-		return NULL;
+		return 0;
 	}
 }
 
-- 
ldv