ASoC: qcom: make osr clock optional

Some LPASS integrations like on APQ8016 do not have OSR clk, so making
osr clk optional would allow such integrations to use lpass driver.

Tested-by: Kenneth Westfield <kwestfie@codeaurora.org>
Acked-by: Kenneth Westfield <kwestfie@codeaurora.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>