ALSA: firewire-lib: fix calculation for size of IR context payload

The quadlets for CIP header is handled as a part of IR context header,
thus it doesn't join in IR context payload. However current calculation
includes the quadlets in IR context payload.

Cc: <stable@vger.kernel.org>
Fixes: f11453c ("ALSA: firewire-lib: use 16 bytes IR context header to separate CIP header")
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20210513125652.110249-5-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/firewire/amdtp-stream.c

@@ -1071,23 +1071,22 @@ static int amdtp_stream_start(struct amdtp_stream *s, int channel, int speed,
 		s->data_block_counter = 0;
 	}
 
-	/* initialize packet buffer */
+	// initialize packet buffer.
+	max_ctx_payload_size = amdtp_stream_get_max_payload(s);
 	if (s->direction == AMDTP_IN_STREAM) {
 		dir = DMA_FROM_DEVICE;
 		type = FW_ISO_CONTEXT_RECEIVE;
-		if (!(s->flags & CIP_NO_HEADER))
+		if (!(s->flags & CIP_NO_HEADER)) {
+			max_ctx_payload_size -= 8;
 			ctx_header_size = IR_CTX_HEADER_SIZE_CIP;
-		else
+		} else {
 			ctx_header_size = IR_CTX_HEADER_SIZE_NO_CIP;
-
-		max_ctx_payload_size = amdtp_stream_get_max_payload(s) -
-				       ctx_header_size;
+		}
 	} else {
 		dir = DMA_TO_DEVICE;
 		type = FW_ISO_CONTEXT_TRANSMIT;
 		ctx_header_size = 0;	// No effect for IT context.
 
-		max_ctx_payload_size = amdtp_stream_get_max_payload(s);
 		if (!(s->flags & CIP_NO_HEADER))
 			max_ctx_payload_size -= IT_PKT_HEADER_SIZE_CIP;
 	}