Use s.c_str() in log messages

Resolves openbmc/openbmc#2905

Tested: static_assert only

Change-Id: Ib39ca78a6edd415263c75175190da3b3ee7ab183
Signed-off-by: Joseph Reynolds <jrey@us.ibm.com>
diff --git a/errors.cpp b/errors.cpp
index 9dbbaf0..ed23ffe 100644
--- a/errors.cpp
+++ b/errors.cpp
@@ -25,7 +25,7 @@
 void InterfaceError::log() const
 {
     logging::log<logging::level::ERR>(
-        what(), phosphor::logging::entry("INTERFACE=%s", interface));
+        what(), phosphor::logging::entry("INTERFACE=%s", interface.c_str()));
 }
 } // namespace manager
 } // namespace inventory