ASoC: mxs: mxs-sgtl5000: Simplify probe function

mxs is a device tree only platform, which allows us to simplify a bit
mxs_sgtl5000_probe(), because there is no need to check whether device tree is
supported or not.

Remove mxs_sgtl5000_probe_dt() and place its content inside mxs_sgtl5000_probe()
for making the code simpler.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Mark Brown <broonie@linaro.org>