[gegl] operations: fix new g_object_ref() warnings

[Michael Natterer <mitch src gnome org>]

commit d7a0d88adc4bb576e0c17bc67ed3d3643643edab
Author: Michael Natterer <mitch gimp org>
Date:   Wed Apr 4 20:20:29 2018 +0200

    operations: fix new g_object_ref() warnings
    
    In latest GLib, g_object_ref() returns the type that was passed in.
    Cast some parameters to match the variable we assign to.

 operations/core/cache.c |    2 +-
 operations/core/nop.c   |    3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/operations/core/cache.c b/operations/core/cache.c
index c630ae2..9ac31a8 100644
--- a/operations/core/cache.c
+++ b/operations/core/cache.c
@@ -62,7 +62,7 @@ process (GeglOperation       *operation,
       g_clear_object (&o->cache);
 
       if (operation->node->cache)
-        o->cache = g_object_ref (operation->node->cache);
+        o->cache = g_object_ref ((GObject *) operation->node->cache);
     }
 
   return TRUE;
diff --git a/operations/core/nop.c b/operations/core/nop.c
index f393c94..d130792 100644
--- a/operations/core/nop.c
+++ b/operations/core/nop.c
@@ -62,7 +62,8 @@ gegl_nop_process (GeglOperation        *operation,
       return FALSE;
     }
 
-  gegl_operation_context_take_object (context, "output", g_object_ref (input));
+  gegl_operation_context_take_object (context, "output",
+                                      g_object_ref ((GObject *) input));
   return TRUE;
 }