ALSA: firewire-lib: drop skip argument from helper functions to queue a packet

On most of audio and music units on IEEE 1394 bus which ALSA firewire stack
supports (or plans to support), CIP with two quadlets header is used.
Thus, there's no cases to queue packets with blank payload. If such packets
are going to be queued, it means that they're for skips of the cycle.

This commit simplifies helper functions to queue a packet.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Acked-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>