LU-16768 lfs: copy optarg string other than using it directly

LU-16768 lfs: copy optarg string other than using it directly

Copy optarg string for fp_format_printf_str lest it be messed
later.

Fixes: 6b8e97b76c ("LU-10378 utils: add formatted printf to lfs find")
Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: Ib32883d3261ae921adf0fdd7b05bcbf728de7557
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50733
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Rick Mohr <mohrrf@ornl.gov>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>