Change InputMessage.motion.pointerSize to a uint32_t.

This ensures it's the same size in both 32 and 64 bit
processes and also brings it in line with struct
MotionEntry.

(cherry-picked from commit bc6001b026069714177526eb1120b0011d6f2a51)

Change-Id: Ide6bb4dc05cc92a7ae8833e615e8ebb2353255a6