ASoC: max98088: Fix logging of hardware revision.

The hardware revision of the codec is based at 0x40.  Subtract that
before convering to ASCII.  The same as it is done for 98095.

Signed-off-by: Dylan Reid <dgreid@chromium.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: stable@vger.kernel.org