chronovu-la: Silence overly verbose log message.

This triggered all kinds of unrelated / confusing log messages
for unrelated hardware devices, e.g.:

  sr: [00:00.613080] chronovu-la: Unknown iProduct string 'USB-based Instrument'.
  sr: [00:00.614374] chronovu-la: Unknown iProduct string 'GL3220      '.
  sr: [00:00.614907] chronovu-la: Unknown iProduct string 'USB 3.0 HUB      '.
  sr: [00:00.615558] chronovu-la: Unknown iProduct string 'USB 2.0 HUB      '.
  sr: [00:00.619846] chronovu-la: Unknown iProduct string 'Bluetooth USB Host Controller'.
  sr: [00:00.620411] chronovu-la: Unknown iProduct string 'USB 3.0 HUB      '.
  sr: [00:00.624293] chronovu-la: Unknown iProduct string 'UAC1 DAC'.
  sr: [00:00.627849] chronovu-la: Unknown iProduct string 'BRCM20702 Hub'.
  sr: [00:00.628640] chronovu-la: Unknown iProduct string 'USB 2.0 HUB      '.
  sr: [00:00.674777] chronovu-la: Unknown iProduct string 'USB2223'.
  sr: [00:00.675034] chronovu-la: Unknown iProduct string ''.
  sr: [00:00.675180] chronovu-la: Unknown iProduct string ''.
  sr: [00:00.675205] hwdriver: Scan found 0 devices (chronovu-la).