package/directfb: Disable dynload when BR2_PREFER_STATIC_LIB is enabled
fixes http://autobuild.buildroot.net/results/a74/a74b97053d7cad4fcce59f658a4b7b4340284b80/
Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>