ALSA: usb-audio: Reorder snd_djm_devices[] entries

Olivia Mackintosh has posted to alsa-devel reporting that
there's a potential bug that could break mixer quirks for Pioneer
devices introduced by 6d277881
"ALSA: usb-audio: Add support for the Pioneer DJM 750MK2
Mixer/Soundcard".

This happened because the DJM 750 MK2 was added last to the Pioneer DJM
device table index and defined as 0x4 but was added to snd_djm_devices[]
just after the DJM 750 (MK1) entry instead of last, after the DJM 900
NXS2. This escaped review.

To prevent that from ever happening again, Takashi Iwai suggested to use
C99 array designators in snd_djm_devices[] instead of simply reordering
the entries.

Fixes: 6d277881 ("ALSA: usb-audio: Add support for the Pioneer DJM 750MK2")
Reported-by: Olivia Mackintosh <livvy@base.nu>
Suggested-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Geraldo Nascimento <geraldogabriel@gmail.com>
Link: https://lore.kernel.org/r/Yau46FDzoql0SNnW@gedaySigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_quirks.c

@@ -3016,11 +3016,11 @@ static const struct snd_djm_ctl snd_djm_ctls_750mk2[] = {
 
 
 static const struct snd_djm_device snd_djm_devices[] = {
-	SND_DJM_DEVICE(250mk2),
-	SND_DJM_DEVICE(750),
-	SND_DJM_DEVICE(750mk2),
-	SND_DJM_DEVICE(850),
-	SND_DJM_DEVICE(900nxs2)
+	[SND_DJM_250MK2_IDX] = SND_DJM_DEVICE(250mk2),
+	[SND_DJM_750_IDX] = SND_DJM_DEVICE(750),
+	[SND_DJM_850_IDX] = SND_DJM_DEVICE(850),
+	[SND_DJM_900NXS2_IDX] = SND_DJM_DEVICE(900nxs2),
+	[SND_DJM_750MK2_IDX] = SND_DJM_DEVICE(750mk2),
 };