ASoC: pcm512x: Trigger auto-increment of register addresses on i2c

When the codec is connected using i2c, it will only auto-increment
register addresses if msb (0x80) of the register address byte is set.

[Fixes cache sync if multiple adjacent registers are updated -- broonie]

Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org