msm: camera: isp: Initialize the isp clock index before enable

During get clock routine there is a possiblity that clock
index that is used for enable clock routine may become
un-initialized with incorrect clock index which might ind-
use zero isp clocks to be enabled and eventually make an
unclocked access. So, initialize clock index correctly ba-
sed on all combinations of clock names for given target
device tree.

Change-Id: I42cc72db45d29d79a84984b10dbb3c9c8112894b
Signed-off-by: Lokesh Kumar Aakulu <lkumar@codeaurora.org>