ALSA: usx2y: Coding style fixes

This patch fixes various trivial coding-style issues in usx2y code,
such as:
* the assginments in if condition
* comparison order with constants
* NULL / zero checks
* unsigned -> unsigned int
* addition of braces in control blocks
* debug print with function names
* move local variables in block into function head
* reduction of too nested indentations

No functional changes.

Link: https://lore.kernel.org/r/20210517131545.27252-4-tiwai@suse.de


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