usign: Revert r47582 "usign: activate format-security checks"

I accidentally deactivated it. This should be set to active it in any case
independently what was set in the user config.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

SVN-Revision: 47587

package/system/usign/Makefile

@@ -10,6 +10,7 @@ PKG_SOURCE_SUBDIR:=$(PKG_NAME)-$(PKG_VERSION)
 PKG_SOURCE_VERSION:=cf8dcdb8a4e874c77f3e9a8e9b643e8c17b19131
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION)-$(PKG_SOURCE_VERSION).tar.gz
 CMAKE_INSTALL:=1
+PKG_CHECK_FORMAT_SECURITY:=1
 PKG_USE_MIPS16:=0
 
 PKG_LICENSE:=ISC