Fix wrong DATADIR variable

Author: ximion

config.h.in

@@ -11,7 +11,7 @@
 #define LOCALEDIR "@CMAKE_INSTALL_FULL_LOCALEDIR@"
 #define PKGLIBDIR "@CMAKE_INSTALL_FULL_LIBEXECDIR@/appstream"
 #define PREFIXDIR "@CMAKE_INSTALL_PREFIX@"
-#define DATADIR "@CMAKE_INSTALL_FULL_DATADIR@/appstream"
+#define DATADIR "@CMAKE_INSTALL_FULL_DATADIR@"
 #define LIBDIR "@CMAKE_INSTALL_FULL_LIBDIR@"
 #define BUILDDIR "@CMAKE_BINARY_DIR@"