ALSA: dice: ensure transmission speed for transmitted packets

As of kernel 4.10, ALSA dice driver is expected to be used in default
speed. In most cases, it's S400. While, IEEE 1394 specification describes
the other speed such as S800.

According to 'TCD30XX User Guide', its link layer controller supports
several transmission speed up to S800[0]. In Dice software interface,
transmission speed in output direction can be configured by asynchronous
transaction to 'TX_SPEED' offset in its address space. S800 may be
available.

This commit improves configuration of transmission unit before starting
packet streaming for this purpose. The value of 'max_speed' in 'fw_device'
data structure has available maximum speed decided in bus arbitration,
thus it's within capacity of the unit.

[0] TCD3xx User Guide - TCAT 1394 LLC, Revision 0.9.0-41360 (TC Applied Technologies, May 6 2015)
http://www.tctechnologies.tc/index.php/support/support-hardware/dice-iii-detailed-documentation



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