clang: ?e64_to_cpu() and cpu_to_?e64(): cast to uint64_t.

clang: ?e64_to_cpu() and cpu_to_?e64(): cast to uint64_t.

On x86_64, clang makes __builtin_bswap64() return "unsigned long"
instead of "unsigned long long", so using PRIx64 complains all over the
place.  Casting to uint64_t satisfies both compilers.

Signed-off-by: Peter Jones <pjones@redhat.com>