ASoC: am3517evm: Do not configure McBSP1 CLKR/FSR signal muxing

The muxing is done at board level, no need to do it in the ASoC machine
driver.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>