ALSA: usb-audio: Apply mutex around snd_usb_endpoint_set_params()

The protection with chip->mutex was lost after splitting
snd_usb_endpoint_set_params() and snd_usb_endpoint_prepare().
Apply the same mutex again to the former function.

Fixes: 2be79d58

 ("ALSA: usb-audio: Split endpoint setups for hw_params and prepare (take#2)")
Link: https://lore.kernel.org/r/20221009104212.18877-3-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>