floss: Properly cast types before logging

On ARM platforms, log messages in the metrics implementation are
crashing because the va_list size isn't correct. This wasn't caught by
-Wformat either and only seen during runtime tests.

Bug: 306240585
Test: mma -j
Test: Run autotest on Kukui with fix
Change-Id: I7a5951021649399ea8574e061d06837a78dc62b9