netfs: Fix proc/fs/fscache symlink to point to "netfs" not "../netfs"

Fix the proc/fs/fscache symlink to point to "netfs" not "../netfs".

Reported-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: Christian Brauner <christian@brauner.io>
cc: linux-fsdevel@vger.kernel.org
cc: linux-cachefs@redhat.com