fix misuse of formatting specifiers

The Clang/GCC formatting warning triggers for usage of %lld with off_t
on 64-bit because it's defined as a long int, not a long long int. It
isn't important, but it's technically undefined.

This fix is in anticipation of adding __attribute__((format(...))) to
many functions where it is currently missing.

Change-Id: I2bf33e6563a2892d2f54d7c582cbdeadf867e84f