uml: fix symlink loops

symlinks to directories in the non-O= case were lacking -n, which meant
that, when the link already existed, a new link pointing at itself was
created in the target directory.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>