Use s.c_str() in log messages

Resolves openbmc/openbmc#2905

Tested: static_assert only

Change-Id: Ib3b74591ca2d26e5f4e0afac508fc248756e0905
Signed-off-by: Joseph Reynolds <jrey@us.ibm.com>
diff --git a/dump_manager.cpp b/dump_manager.cpp
index 4d0904c..15df65b 100644
--- a/dump_manager.cpp
+++ b/dump_manager.cpp
@@ -119,7 +119,7 @@
           (match.size() > 0)))
     {
         log<level::ERR>("Invalid Dump file name",
-                        entry("FILENAME=%s", file.filename()));
+                        entry("FILENAME=%s", file.filename().c_str()));
         return;
     }