[PATCH] ALSA: usb-audio: fix feature unit parser for UAC2

[Daniel Mack]

Fix a small off-by-one bug which causes the feature unit to announce a
wrong number of channels. This leads to illegal requests sent to the
firmware eventually.

Signed-off-by: Daniel Mack <daniel at caiaq.de>
---
 sound/usb/mixer.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 97dd176..03ce971 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1126,7 +1126,7 @@ static int parse_audio_feature_unit(struct mixer_build *state, int unitid, void
 	} else {
 		struct uac2_feature_unit_descriptor *ftr = _ftr;
 		csize = 4;
-		channels = (hdr->bLength - 6) / 4;
+		channels = (hdr->bLength - 6) / 4 - 1;
 		bmaControls = ftr->bmaControls;
 	}
 
-- 
1.7.1