msm: kgsl: use div64_s64 instead of do_div

Fix compiler warning about invalid use of do_div macro.
Use div64_s64 function to divide signed 64-bit numbers.

Change-Id: I817cc363097c4b98d10ef8450acfc4061eacd3d0
Signed-off-by: Maria Yu <aiquny@codeaurora.org>