ASoC: samsung: Drop uneeded RCLKSRC setting in the Snow driver

The RCLKSRC mux input 0 is a default configuration after reset, so
there is no need for this explicit snd_soc_dai_set_sysclk() call.
Also, this static mux clock configuration can be specified in DT.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>