gpu: ion: Use correct type for variables

Use correct type for variables to prevent overflow of signed
type when assiging from an unsigned type.

Change-Id: I0055d35c7310d111de590db3798950fd98f1b298
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>
Merge "gpu: ion: Use correct type for variables" into jb4.2