msm: cpp: Retrieve clock index from dtsi clock name

The clock used to enable cpp hadware can be different
for the different platform. To get the indexes od the
clock that are set by cpp driver, we have to use their
names. The only requirement is that these clocks have
to be called with the same names accross the platforms.

Signed-off-by: Iliya Varadzhakov <ivarad@codeaurora.org>
Change-Id: I8a4612cd0ae227dad0e2538af64ea75da64f35f2