include/linux/usb/audio-v2.h: add more UAC2 details

Also, remove the 'bmControl' field from uac_clock_selector_descriptor,
which was at the wrong offset. This struct is currently unused.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>