[ALSA] snd_usb_caiaq_input_free() fix

input_free_device()'s comment says:
input_free_device() should only be used if input_register_device() was
not called yet or if it failed. Once device was registered
use input_unregister_device() and memory will be freed once last
refrence to the device is dropped.

Signed-off-by: Karsten Wiese <fzu@wemgehoertderstaat.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>