ucert: add PROVIDES also for minimal 'ucert' package

Otherwise ucert-full gets selected instead of ucert when depending on
ucert.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

package/system/ucert/Makefile

@@ -47,6 +47,7 @@ define Package/ucert
   CATEGORY:=Base system
   DEPENDS:=+usign +libubox
   TITLE:=OpenWrt certificate verification utility
+  PROVIDES:=ucert
   CONFLICTS:=ucert-full
   VARIANT:=tiny
 endef