webkitgtk24: depend on x11 backend for gtk3

The other rendering backends aren't supported right now, so depend on
the X11 one to avoid build breakage. Fixes:
http://autobuild.buildroot.net/results/1b3/1b372dd04eaccd8a9d24390d509b0a49f692746c/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/webkitgtk24/webkitgtk24.mk

@@ -101,7 +101,7 @@ endif
 # webkit1 (old API) uses gtk2, webkit2 (new API) uses gtk3
 # Both can be built simultaneously, prefer "newer" for size/time savings
 # gtk2 is mandatory for plugin support
-ifeq ($(BR2_PACKAGE_LIBGTK3),y)
+ifeq ($(BR2_PACKAGE_LIBGTK3_X11),y)
 WEBKITGTK24_CONF_OPTS += \
 	--with-gtk=3.0 \
 	--disable-webkit1