LU-11839 iokit: Fix help message

LU-11839 iokit: Fix help message

This patch fixes help message of iokit-gather-stats
to properly add "--help" instead of "-help". Two
hyphen/dashes are expected by getopts.

Test-Parameters: trivial
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: I64270598fc19377571b68066d617b50fcb48cc12
Reviewed-on: https://review.whamcloud.com/43114
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>