ALSA: usb-audio: Correct the return code from snd_usb_endpoint_set_params()

snd_usb_endpoint_set_params() should return zero for a success, but
currently it returns the sample rate.  Correct it.

Fixes: 2be79d58

 ("ALSA: usb-audio: Split endpoint setups for hw_params and prepare (take#2)")
Link: https://lore.kernel.org/r/20221009104212.18877-4-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>