Documentation/accounting/getdelays.c: fix endless loop

When no option is passed to getdelays it just hangs, waiting
for a reply which will never come.

This patch prints usage() when no output marker is specified.

Signed-off-by: Marcus Meissner <meissner@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>