yad: fix libgtk3 dependency

Make it depend explicitly on BR2_PACKAGE_LIBGTK3_X11 (the X11 backend
option) to avoid the checker from complaining.
Also add a comment about yad requiring the X11 backend otherwise it's
ambiguous if a user has libgtk3 enabled with broadway/wayland and the
comment shows up. Fixes:
http://autobuild.buildroot.net/results/84d/84d97bbcc0ea4f8eaa50dd25bf9ee8fdee4b937f/

Also cleanup some tiny whitespace in the package mk file.

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

package/yad/Config.in

@@ -1,13 +1,13 @@
 config BR2_PACKAGE_YAD
 	bool "yad"
 	depends on BR2_PACKAGE_XORG7
-	depends on BR2_PACKAGE_LIBGTK2 || BR2_PACKAGE_LIBGTK3
+	depends on BR2_PACKAGE_LIBGTK2 || BR2_PACKAGE_LIBGTK3_X11
 	help
 	  YAD (yet another dialog) is a tool for create graphical dialogs
 	  from shell scripts.
 
 	  http://sourceforge.net/projects/yad-dialog/
 
-comment "yad needs libgtk2 or libgtk3"
+comment "yad needs libgtk2 or libgtk3 w/ X11 backend"
 	depends on BR2_PACKAGE_XORG7
-	depends on !BR2_PACKAGE_LIBGTK2 && !BR2_PACKAGE_LIBGTK3
+	depends on !BR2_PACKAGE_LIBGTK2 && !BR2_PACKAGE_LIBGTK3_X11

package/yad/yad.mk

@@ -10,7 +10,6 @@ YAD_SITE = http://sourceforge.net/projects/yad-dialog/files
 YAD_LICENSE = GPLv3
 YAD_LICENSE_FILES = COPYING
 YAD_DEPENDENCIES = host-intltool host-pkgconf
-
 YAD_CONF_OPTS = --enable-html=no
 
 ifeq ($(BR2_PACKAGE_LIBGTK3_X11),y)