Fix inconsistent #include style

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>
diff --git a/clients/dnd.c b/clients/dnd.c
index 5bfe31c..db794fd 100644
--- a/clients/dnd.c
+++ b/clients/dnd.c
@@ -32,7 +32,7 @@
 #include <sys/epoll.h>
 #include <gdk-pixbuf/gdk-pixbuf.h>
 
-#include "wayland-client.h"
+#include <wayland-client.h>
 
 #include "window.h"
 #include "cairo-util.h"