UBUNTU: [Debian] remove the kernel-image firmware list on clean

Signed-off-by: Andy Whitcroft <apw@canonical.com>

debian/rules

@@ -64,6 +64,8 @@ clean: debian/control
 
 	# d-i stuff
 	rm -rf $(DEBIAN)/d-i-$(arch)
+	# Generated on the fly.
+	rm -f $(DEBIAN)/d-i/firmware/kernel-image
 
 	# normal build junk
 	rm -rf $(DEBIAN)/abi/$(release)-$(revision)