Fix signed/unsigned conversion warning

sizeof(T) hands back size_t; clang got upset that we were comparing it
to an int.

Bug: None
Test: mma. Warning disappeared.
Change-Id: I8f201f85a03fcf1070a091a5692eeb00ec13961c
Merged-In: I8f201f85a03fcf1070a091a5692eeb00ec13961c
(cherry picked from commit d3f1401b)