ALSA: firewire-lib: change structure member with proper type

The 'amdtp_stream' structure is initialized by a call of
'amdtp_stream_init()'. Although a parameter of this function is for bit
flags of packet attributes, its type is enumerator.

This commit changes the type so that it's proper for a bit flags.

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