Always use unsigned char char is unsigned by default on ARM, so make it so on other architectures as well Bug: 37208566 Test: ran poc with and without change, ran CTS on x86 and ARM Change-Id: I264db1dad884de7fd8f932cd9571199a1c517f6a (cherry picked from commit 5c9670f28eb7fe59f053f1ad81dff8a716b8aa9d)