fru-device: add extra debug print

Let the user known when the header checksum is invalid.

Change-Id: I6dc97e88987819291197b5c824f5d1fcbc9348ec
Signed-off-by: James Feist <james.feist@linux.intel.com>
diff --git a/src/FruDevice.cpp b/src/FruDevice.cpp
index a5e5c80..9ca578d 100644
--- a/src/FruDevice.cpp
+++ b/src/FruDevice.cpp
@@ -209,6 +209,11 @@
                 }
                 devices->emplace(ii, device);
             }
+            else
+            {
+                std::cerr << "Illegal header checksum at bus " << bus
+                          << " address " << ii << "\n";
+            }
         }
         return 1;
     });