clk: Consolidate recalc rate logic

clk: Consolidate recalc rate logic

The same if-else statement exists four times to recalculate the
rate of a clock. Consolidate this logic into a single function to
save some lines.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>