Print the errno from a fail in the journal

When a file access fails, print the errno of the failure in the same
journal entry the filename is already printed.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I20d268f563cf1bbfa2a5f9780c02998d075f5275
diff --git a/mainloop.cpp b/mainloop.cpp
index b694261..3e7e0bf 100644
--- a/mainloop.cpp
+++ b/mainloop.cpp
@@ -240,7 +240,9 @@
             xyz::openbmc_project::Sensor::Device::ReadFailure::
                 CALLOUT_DEVICE_PATH(_devPath.c_str()));
 
-        log<level::INFO>(fmt::format("Failing sysfs file: {}", file).c_str());
+        log<level::INFO>(fmt::format("Failing sysfs file: {} errno: {}", file,
+                                     e.code().value())
+                             .c_str());
         exit(EXIT_FAILURE);
     }
     auto sensorValue = valueInterface->value();
@@ -530,8 +532,9 @@
                 xyz::openbmc_project::Sensor::Device::ReadFailure::
                     CALLOUT_DEVICE_PATH(_devPath.c_str()));
 
-            log<level::INFO>(
-                fmt::format("Failing sysfs file: {}", file).c_str());
+            log<level::INFO>(fmt::format("Failing sysfs file: {} errno: {}",
+                                         file, e.code().value())
+                                 .c_str());
 
             exit(EXIT_FAILURE);
         }