exception: add errno

NotFoundException inherits from an sdbusplus exception, which
now requires a 'get_errno' interface.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I549f26a0f2096df3be6cc05870c58755e46f393b
diff --git a/src/main.cpp b/src/main.cpp
index be24368..37f216f 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -39,6 +39,11 @@
         return "xyz.openbmc_project.Common.Error.ResourceNotFound: "
                "The resource is not found.";
     };
+
+    int get_errno() const noexcept override
+    {
+        return ENOENT;
+    }
 };
 
 void update_owners(sdbusplus::asio::connection* conn,