ALSA: snd-usb-caiaq: Set default input mode of A4DJ

Do not start the device with input mode undefined. Mimic the behaviour of
the Audio 8 DJ and start in phono input mode.

Signed-off-by: Mark Hills <mark@pogo.org.uk>
Acked-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>