udev/scsi_id: increase MAX_SERIAL_LEN from 256 to 512

udev/scsi_id: increase MAX_SERIAL_LEN from 256 to 512

The current MAX_SERIAL_LEN value of 256 is insufficient for some SCSI
devices with non-standard serial number lengths. In do_scsi_page80_inquiry(),
the required buffer length is calculated as:

    len = 1 + VENDOR_LENGTH + MODEL_LENGTH + buf[3]
        = 1 + 8 + 16 + buf[3]
        = 25 + buf[3]

where buf[3] contains the serial number length reported by the device.
According to the SCSI specification, this field is an unsigned 8-bit
value, meaning it can theoretically be up to 255 bytes. This results
in a maximum required length of 280 bytes, exceeding the current limit
of 256 bytes.

When this occurs, scsi_id fails with an error message like:
    "length 256 too short - need 280"

This has been observed with certain vendor devices that report unusually
long serial numbers in VPD page 0x80.

Increase MAX_SERIAL_LEN to 512 to accommodate the maximum possible
serial number length plus all required prefixes (vendor, model, and
type identifiers), providing sufficient headroom for non-compliant
devices while maintaining reasonable memory usage.

Signed-off-by: tuhaowen <tuhaowen@uniontech.com>