Fix build error in debug

std::exception doesn't have a direct conversion to iostream.  This only
shows up when building for debug.

Tested:
Forced -DCMAKE_BUILD_TYPE=Debug, and verified code builds.

Signed-off-by: Ed Tanous <ed@tanous.net>
Change-Id: I6fdd0e561f1cecc5f40f0e8b9c624f746ce6456f
diff --git a/http/http_connection.h b/http/http_connection.h
index 679140c..109a272 100644
--- a/http/http_connection.h
+++ b/http/http_connection.h
@@ -549,7 +549,7 @@
                 }
                 catch (std::exception& p)
                 {
-                    BMCWEB_LOG_ERROR << p;
+                    BMCWEB_LOG_ERROR << p.what();
                 }
 
                 crow::authorization::authenticate(*req, res, session);