[gnome-control-center] printers: Fix compilation warning

[Marek Kašík <mkasik src gnome org>]

commit 77750c507615788d46ec66a25368fe4aa4a83966
Author: Marek Kasik <mkasik redhat com>
Date:   Tue Sep 20 12:29:09 2016 +0200

    printers: Fix compilation warning
    
    We need to include cups/ppd.h explicitly due to some modification
    of structure of CUPS headers

 panels/printers/cc-printers-panel.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/panels/printers/cc-printers-panel.c b/panels/printers/cc-printers-panel.c
index 4c88223..fb55608 100644
--- a/panels/printers/cc-printers-panel.c
+++ b/panels/printers/cc-printers-panel.c
@@ -29,6 +29,7 @@
 #include <gdesktop-enums.h>
 
 #include <cups/cups.h>
+#include <cups/ppd.h>
 
 #include <math.h>