start-stop-daemon: fix --help: -K or -S is required

function                                             old     new   delta
.rodata                                           105381  105382      +1
packed_usage                                       34638   34602     -36
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/1 up/down: 1/-36)             Total: -35 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>