ASoC: max98088: Fix logging of hardware revision.

commit 98682063 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>