ALSA: firewire-lib: pass data block count as an argument to tracepoints event

This is a preparation for future commit that 'struct
amdtp_stream.data_block_count' does not represent the value of
data block count for current data block.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>