firewire-lib: remove needless initialization for MIDI stuff

struct snd_efw is kept by snd_card_create(). This function keeps memory with
zcalloc so the content is zero-ed. In this reason, initialization for MIDI is
needless.
fireworks/bebob: fix compiling warning

Each module has 'enable' local variable to switch enable/disable the module.
Even if it's registered as 'bool' type option, it's declared as 'int'.
fireworks: shorten the name of 'connection' member

'input_connection' to 'in_conn'
'output_connection' to 'out_conn'
fireworks: change the timing to start stream

Start streaming should be a part of pcm_prepare process.
bebob: enable Firewire 410 to be proved

Firewire 410 with firmware version 5058 has a different vendor id.