LU-17673 obdclass: properly free opts string

LU-17673 obdclass: properly free opts string

With lmd_parse() rework being based on the llite match_table work
it inherited the same memory leak. Save the opts pointer to be
used bu kfree at the end.

Fixes: 415fa27540 ("LU-9325 obdclass: use match_table for server mount options")
Test-Parameters: trivial
Change-Id: I016f39f1512118486a0dc119ab075a1408b2a709
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54650
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>