package/transmission: fix gtk support

Gtk support is controlled by ARG_WITH since
https://github.com/transmission/transmission/commit/2ccc2bbbfe2e4a26dfeaa13b56c412ea0af4ebe4

Fixes a build error if libgtk2/3 was built before transmission:
http://autobuild.buildroot.net/results/6b6/6b6ce352a9edfe3aaba82be143092a878e7715ed/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/transmission/transmission.mk

@@ -82,10 +82,10 @@ TRANSMISSION_CONF_OPTS += --disable-remote
 endif
 
 ifeq ($(BR2_PACKAGE_TRANSMISSION_GTK),y)
-TRANSMISSION_CONF_OPTS += --enable-gtk
+TRANSMISSION_CONF_OPTS += --with-gtk
 TRANSMISSION_DEPENDENCIES += libgtk2
 else
-TRANSMISSION_CONF_OPTS += --disable-gtk
+TRANSMISSION_CONF_OPTS += --without-gtk
 endif
 
 $(eval $(autotools-package))