usb: audio-v2: Correct the comment for struct uac_clock_selector_descriptor

The comment in UAC2 clock selector descriptor definition mentions the
bAssocTerminal after baCSourceID[], but it doesn't exist in the actual
definition.  Let's correct it.

Fixes: 5dd360eb ("include/linux/usb/audio-v2.h: add more UAC2 details")
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>