Use size_t instead of uint

uint isn't a standard type, use size_t instead.  Fixes building against
musl libc, which doesn't define uint unless _GNU_SOURCE or _BSD_SOURCE
is defined.

Bug: 190084016
Test: m USE_HOST_MUSL=true host-native
Change-Id: I2a1aac6d7a4f780dcc6db0266de0bf49015d4437