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

Do not explicity set the default input mode. Use the hardware default
of mode 0 ('Control vinyl'), which is now available.

This reverts commit e3ca4c99.

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