libssh: mark as BROKEN due to CVE-2018-10933

The only known user of this library is currently unable to get their
application to work with with the fixed 0.7.6 release of this library.

To prevent accidental use by unknown parties of a flawed library, mark
it as BROKEN.

Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>

libs/libssh/Makefile

@@ -32,7 +32,7 @@ define Package/libssh
   CATEGORY:=Libraries
   URL:=$(PKG_SOURCE_URL)
   TITLE:=SSH library
-  DEPENDS:=+libpthread +librt +zlib +libopenssl
+  DEPENDS:=+libpthread +librt +zlib +libopenssl @BROKEN
 endef
 
 define Package/libssh/description