ASoC: tas6424: Add channel fault reporting

The TAS6426 has a register that reports channel faults such as
overcurrent and continuous DC output. Add reporting of this here.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
(cherry picked from commit 5fb6589a)
Signed-off-by: Dan Murphy <dmurphy@ti.com>