caching parent clocks makes sense only when a clock has more
than one parent (mux clocks).
Avoid doing this for every other clock.
Signed-off-by: NRajendra Nayak <rnayak@ti.com>
[mturquette@linaro.org: removed extra parentheses]
Signed-off-by: NMike Turquette <mturquette@linaro.org>