update-alternatives: use package created by opkg-utils

In daisy update-alternatives has been moved from opkg to the opkg-utils recipe.
opkg-utils now creates an additional package update-alternatives-opkg.

Without this patch the opkg-utils recipe is built and the opkg-utils package is
installed for VIRTUAL-RUNTIME_update-alternatives.

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>