Commit d7986405 added a dedicated phony line for cscope.

Fixes: d7986405 ("Makefile: Add back TAGS/ctags/cscope rules")
Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <159916246865.691541.16619858522304817323.stgit@bahia.lan>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>