Use s.c_str() in log messages

Partly resolves openbmc/openbmc 2905

Bonus!  The new static_assert found a related bug in log.cpp:
  log("msg", entry("fmt", data, entry("fmt", data)))
which should have been:
  log("msg", entry("fmt", data), entry("fmt", data))

Tested: static_assert only

Change-Id: Ie1c550a27f454ef92ee096d812adcc400a1a25cf
Signed-off-by: Joseph Reynolds <jrey@us.ibm.com>
1 file changed