[goffice] Compilation: fix warnings.

[Morten Welinder <mortenw src gnome org>]

commit f4f539f7cb438d82131b37940436cacfc3d8b096
Author: Morten Welinder <terra gnome org>
Date:   Sat Dec 2 12:57:05 2017 -0500

    Compilation: fix warnings.

 plugins/plot_xy/gog-xy.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/plugins/plot_xy/gog-xy.c b/plugins/plot_xy/gog-xy.c
index 8d11d74..99a2208 100644
--- a/plugins/plot_xy/gog-xy.c
+++ b/plugins/plot_xy/gog-xy.c
@@ -1140,7 +1140,7 @@ gog_xy_view_render (GogView *view, GogViewAllocation const *bbox)
                                path = gog_chart_map_make_path (chart_map, x_vals, y_vals,
                                                                n, series->base.interpolation,
                                                                series->base.interpolation_skip_invalid,
-                                                               &series->clamped_derivs);
+                                                               (gpointer)&series->clamped_derivs);
 
                        next_path = NULL;
 
@@ -1171,7 +1171,7 @@ gog_xy_view_render (GogView *view, GogViewAllocation const *bbox)
                                                        (chart_map, next_x_vals, next_y_vals,
                                                         next_n_points, next_series->base.interpolation,
                                                         series->base.interpolation_skip_invalid,
-                                                        &series->clamped_derivs);
+                                                        (gpointer)&series->clamped_derivs);
 
                                        }
                                }