[PGO] Fix the type of the formated variable

Change the format type of Value to PRIu64 since it is a uint64_t.
The problem was detected on mips boards building 32-bit binaries,
where it was printing junk values and causing test failure.

Patch by Milos Stojanovic.

Differential Revision: https://reviews.llvm.org/D57583

llvm-svn: 353194