apk: disable rootfs repositories during build

Since we set the root for APK it tries to use those during the build,
which shouldn't happen since local package are used instead.

Disable the repositories by manually setting an empty repository.

Signed-off-by: Paul Spooren <mail@aparcar.org>

include/rootfs.mk

@@ -47,6 +47,7 @@ apk = \
   IPKG_INSTROOT=$(1) \
   $(FAKEROOT) $(STAGING_DIR_HOST)/bin/apk \
 	--root $(1) \
+	--repositories-file /dev/zero \
 	--keys-dir $(TOPDIR) \
 	--no-cache \
 	--no-logfile \