clk: correct comments for __clk_determine_rate

Correct comments for __clk_determine_rate.

Signed-off-by: Peng Fan <van.freenix@gmail.com>
Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>