ASoC: tegra: always use clk_get() in utility code

Now that all of the Tegra device trees have been updated to represent
the required audio clocks, remove the compatibility code from the Tegra
ASoC utility code, and always use clk_get() rather than clk_get_sys().

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>