Makefile: fixup previous 'make clean' fix

Apparently, Makefile comments need to be made without indentation. Otherwise,
they are printed out as shell commands. This fix prevents seeing this in your
shell during 'make clean':

  $ make clean
  ...
  # findutils v4.1.x (RHEL 4) do not have '+' syntax
  ...

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Acked-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>