Change return codes to match sd-bus convention

in sd-bus callbacks we should be following the same conventions as
sd-bus, returning 0 for success, and returning some correct errno for
failure.  This changes the couple spots I found to follow that
convention.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: I9914e35d4938e31c2d94c4f165108606263ac0e7
diff --git a/include/sdbusplus/asio/detail/async_send_handler.hpp b/include/sdbusplus/asio/detail/async_send_handler.hpp
index 0f40ce9..dafc7a8 100644
--- a/include/sdbusplus/asio/detail/async_send_handler.hpp
+++ b/include/sdbusplus/asio/detail/async_send_handler.hpp
@@ -41,7 +41,7 @@
     {
         if (userdata == nullptr)
         {
-            return -1;
+            return -EINVAL;
         }
 
         // Take RAII ownership of the pointer again
@@ -50,13 +50,13 @@
 
         if (mesg == nullptr)
         {
-            return -1;
+            return -EINVAL;
         }
         message_t message(mesg);
         auto ec = make_error_code(
             static_cast<boost::system::errc::errc_t>(message.get_errno()));
         context->handler_(ec, message);
-        return 1;
+        return 0;
     }
 };