ASoC: davinci-mcasp: don't configure AFSX direction in DIT mode

AFSX won't be used in DIT mode. The related pins are AHCLKX and
the data pins.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Acked-by: Vaibhav Bedia <vaibhav.bedia@ti.com>
Tested-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>