package/gst1-plugins-bad: fix decklink comment

It was missing the dependency on the toolchain features.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/gstreamer1/gst1-plugins-bad/Config.in

@@ -346,6 +346,7 @@ config BR2_PACKAGE_GST1_PLUGINS_BAD_PLUGIN_DECKLINK
 	  Blackmagic Decklink plugin
 
 comment "decklink requires a toolchain with C++ support enabled"
+	depends on !BR2_INSTALL_LIBSTDCPP
 
 config BR2_PACKAGE_GST1_PLUGINS_BAD_PLUGIN_DIRECTFB
 	bool "directfb"