BACKPORT: ASoC: max98088: Fix logging of hardware revision.

BACKPORT: 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.

BUG=chrome-os-partner:18551
TEST=check dmesg and see revision = 'A'

Signed-off-by: Dylan Reid <dgreid@chromium.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
(cherry picked from commit 98682063549bedd6e2d2b6b7222f150c6fbce68c)

Change-Id: I942d832bceb9c42370a0dd8364040b157d7ffd77
Reviewed-on: https://gerrit.chromium.org/gerrit/48462
Reviewed-by: Chih-Chung Chang <chihchung@chromium.org>
Commit-Queue: Dylan Reid <dgreid@chromium.org>
Tested-by: Dylan Reid <dgreid@chromium.org>