ALSA: usb-audio: Check shutdown at endpoint_set_interface()

The call of usb_set_interface() and a delay are superfluous when the
device has been already disconnected.  Add a disconnection check
before doing it.

Link: https://patch.msgid.link/20240808091522.31415-1-tiwai@suse.de


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