toplevel.mk: add target feeds in 'make distclean'

When 'make distclean' is called, remove the target feeds.
Otherwise the directory target/linux/feeds/ (with broken symlinks) still
exists after a distclean.

Signed-off-by: Thomas Richard <[email protected]>
Link: https://patchwork.ozlabs.org/project/openwrt/patch/[email protected]/
Signed-off-by: Hauke Mehrtens <[email protected]>

include/toplevel.mk

@@ -276,7 +276,7 @@ help:
 	cat README.md
 
 distclean:
-	rm -rf bin build_dir .ccache .config* dl feeds key-build* logs package/feeds staging_dir tmp
+	rm -rf bin build_dir .ccache .config* dl feeds key-build* logs package/feeds target/linux/feeds staging_dir tmp
 	@$(_SINGLE)$(SUBMAKE) -C scripts/config clean
 
 ifeq ($(findstring v,$(DEBUG)),)