ALSA: firewire-motu: fix construction of PCM frame for capture direction

commit f97a0944 upstream.

In data blocks of common isochronous packet for MOTU devices, PCM
frames are multiplexed in a shape of '24 bit * 4 Audio Pack', described
in IEC 61883-6. The frames are not aligned to quadlet.

For capture PCM substream, ALSA firewire-motu driver constructs PCM
frames by reading data blocks byte-by-byte. However this operation
includes bug for lower byte of the PCM sample. This brings invalid
content of the PCM samples.

This commit fixes the bug.
Reported-by: Peter Sjöberg <autopeter@gmail.com>
Cc: <stable@vger.kernel.org> # v4.12+
Fixes: 4641c939 ("ALSA: firewire-motu: add MOTU specific protocol layer")
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

sound/firewire/motu/amdtp-motu.c

@@ -136,7 +136,9 @@ static void read_pcm_s32(struct amdtp_stream *s,
 		byte = (u8 *)buffer + p->pcm_byte_offset;
 
 		for (c = 0; c < channels; ++c) {
-			*dst = (byte[0] << 24) | (byte[1] << 16) | byte[2];
+			*dst = (byte[0] << 24) |
+			       (byte[1] << 16) |
+			       (byte[2] << 8);
 			byte += 3;
 			dst++;
 		}