ALSA: usb-audio: Add Pioneer DJM-450 mixer controls

These values mirror those of the Pioneer DJM-250MK2 as the channel layout
appears identical based on my observations. This duplication could be removed in
later contributions if desired.

Signed-off-by: Sarah Grant <s@srd.tw>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20231201181654.5058-1-s@srd.tw


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