build: cleanup tmp/ dir of target rootfs

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

include/rootfs.mk

@@ -80,6 +80,7 @@ define prepare_rootfs
 	@-find $(1) -name .svn  | $(XARGS) rm -rf
 	@-find $(1) -name .git  | $(XARGS) rm -rf
 	@-find $(1) -name '.#*' | $(XARGS) rm -f
+	rm -rf $(1)/tmp/*
 	rm -f $(1)/usr/lib/opkg/lists/*
 	rm -f $(1)/usr/lib/opkg/info/*.postinst*
 	rm -f $(1)/usr/lib/opkg/info/*.prerm*