openssl-format-source: no dash marker on *INDENT-(ON|OFF)* comments

We mark small comments with a dash immediately following the starting /*.
However, *INDENT-(ON|OFF)* comments shouldn't be treated that way, or
indent will ignore them if we do.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>