ALSA: usx2y: Cleanup probe and disconnect callbacks

Minor code refactoring by merging the superfluous function calls.
The functions were split in the past for covering pre-history USB
driver code, but this is utterly useless.

Link: https://lore.kernel.org/r/20210517131545.27252-11-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>