ASoC: tas2770: Fix snd_soc_update_bits error handling

ASoC: tas2770: Fix snd_soc_update_bits error handling

According the documentation for snd_soc_update_bits the API
will return a 1 if the update was successful with a value change,
a 0 if the update was successful with no value change or a negative
if the command just failed.

So the value of return in the driver needs to be checked for being less
then 0 or the caller may indicate failure when the value actually
changed.

Signed-off-by: Dan Murphy <dmurphy@ti.com>
Link: https://lore.kernel.org/r/20191007171157.17813-1-dmurphy@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>