clk: asm9260: Use parent accuracy in fixed rate clk

This fixed rate clk is registered with the accuracy of the parent. Use
CLK_FIXED_RATE_PARENT_ACCURACY for that instead of getting the parent
clk and finding out the accuracy that way.

Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Link: https://lkml.kernel.org/r/20190830150923.259497-10-sboyd@kernel.org