msm: camera: isp: fix isp bus clock calculation

ISP send too big numbers for bus update, which were discarded and
clock was not updated. This fix corrects ISP bus clock result, using
proper 64bit operations.

Change-Id: I763d8a508283f74fc0a8538e23a8f81facbc6d3a
Signed-off-by: Petar Sivenov <psiven@codeaurora.org>