ALSA: HDSP: check for io box before uploading firmware

currently the hdsp driver tries to upload the firmware, even if the
io box is not connected. this patch adds a check for the io box
before trying to upload the firmware.
thus instead of messages complaining about the fifo status and firmware
loading failure, the driver gives a message that no multiface or
digiface is connected.

[A minor coding-style fix by tiwai]

Signed-off-by: Tim Blechmann <tim@klingt.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>