Revert "ALSA: usb-audio: purge needless variable length array"

This reverts commit 89b593c30e83 ("ALSA: usb-audio: purge needless
variable length array").  The patch turned out to cause a severe
regression, triggering an Oops at snd_usb_ctl_msg().  It was overseen
that snd_usb_ctl_msg() writes back the response to the given buffer,
while the patch changed it to a read-only const buffer.  (One should
always double-check when an extra pointer cast is present...)

As a simple fix, just revert the affected commit.  It was merely a
cleanup.  Although it brings VLA again, it's clearer as a fix.  We'll
address the VLA later in another patch.

Fixes: 89b593c30e83 ("ALSA: usb-audio: purge needless variable length array")
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=195875
Cc: <stable@vger.kernel.org> # v4.11+
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_us16x08.c

@@ -698,12 +698,12 @@ static int snd_us16x08_meter_get(struct snd_kcontrol *kcontrol,
 	struct snd_usb_audio *chip = elem->head.mixer->chip;
 	struct snd_us16x08_meter_store *store = elem->private_data;
 	u8 meter_urb[64];
-	char tmp[sizeof(mix_init_msg2)] = {0};
+	char tmp[max(sizeof(mix_init_msg1), sizeof(mix_init_msg2))];
 
 	switch (kcontrol->private_value) {
 	case 0:
-		snd_us16x08_send_urb(chip, (char *)mix_init_msg1,
-				     sizeof(mix_init_msg1));
+		memcpy(tmp, mix_init_msg1, sizeof(mix_init_msg1));
+		snd_us16x08_send_urb(chip, tmp, 4);
 		snd_us16x08_recv_urb(chip, meter_urb,
 			sizeof(meter_urb));
 		kcontrol->private_value++;
@@ -721,7 +721,7 @@ static int snd_us16x08_meter_get(struct snd_kcontrol *kcontrol,
 	case 3:
 		memcpy(tmp, mix_init_msg2, sizeof(mix_init_msg2));
 		tmp[2] = snd_get_meter_comp_index(store);
-		snd_us16x08_send_urb(chip, tmp, sizeof(mix_init_msg2));
+		snd_us16x08_send_urb(chip, tmp, 10);
 		snd_us16x08_recv_urb(chip, meter_urb,
 			sizeof(meter_urb));
 		kcontrol->private_value = 0;