ALSA: firewire-lib: fix wrong assignment for 'out_packet_without_header' tracepoint

An initial commit to add tracepoints for packets without CIP headers
introduces a wrong assignment to 'data_blocks' value of
'out_packet_without_header' tracepoint.

This commit fixes the bug.

Cc: <stable@vger.kernel.org> # v4.12+
Fixes: b164d2fd ('ALSA: firewire_lib: add tracepoints for packets without CIP headers')
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>