clk: fixed-rate: Document that accuracy isn't a rate

This kernel-doc talks about a rate for the accuracy. That's wrong.

Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Link: https://lkml.kernel.org/r/20190830150923.259497-9-sboyd@kernel.org