ASoC: tlv320adcx140: Add tx offset slot programming

Add the TX offset slot programming.  There is no RX offset slot
register.

Since there is no RX offset the check for slot symmetry can be removed.

Signed-off-by: Dan Murphy <dmurphy@ti.com>
Link: https://lore.kernel.org/r/20200709185129.10505-2-dmurphy@ti.com


Signed-off-by: Mark Brown <broonie@kernel.org>