xwayland: Staticize weston_wm_set_selection and read_and_dump_property

Signed-off-by: Tiago Vignatti <tiago.vignatti@intel.com>
diff --git a/src/xwayland/window-manager.c b/src/xwayland/window-manager.c
index 9f01c82..303ef15 100644
--- a/src/xwayland/window-manager.c
+++ b/src/xwayland/window-manager.c
@@ -268,7 +268,7 @@
 	}
 }
 
-void
+static void
 read_and_dump_property(struct weston_wm *wm,
 		       xcb_window_t window, xcb_atom_t property)
 {