ALSA: usb-mixer: us16x08: validate meter packet indices

In the Linux kernel, the following vulnerability has been resolved:

ALSA: usb-mixer: us16x08: validate meter packet indices

get_meter_levels_from_urb() parses the 64-byte meter packets sent by

the device and fills the per-channel arrays meter_level[],

comp_level[] and master_level[] in struct snd_us16x08_meter_store.

Currently the function derives the channel index directly from the

meter packet (MUB2(meter_urb, s) - 1) and uses it to index those

arrays without validating the range. If the packet contains a

negative or out-of-range channel number, the driver may write past

the end of these arrays.

Introduce a local channel variable and validate it before updating the

arrays. We reject negative indices, limit meter_level[] and

comp_level[] to SND_US16X08_MAX_CHANNELS, and guard master_level[]

updates with ARRAY_SIZE(master_level).