ASoC: sam9g20ek: Let device core handle pinctrl

Since commit ab78029e

 (drivers/pinctrl: grab default handles from device
core) we can rely on device core for handling pinctrl so remove
devm_pinctrl_get_select_default() from the driver.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Tested-by: Bo Shen <voice.shen@atmel.com>
Acked-by: Bo Shen <voice.shen@atmel.com>