LU-16558 mdt: Fix max limit for "max_mod_rpcs_in_flight"

LU-16558 mdt: Fix max limit for "max_mod_rpcs_in_flight"

This minor fix fixes a bug with the definition of the maximum
limit for the mdt_max_mod_rpcs_in_flight parameter when it is
changed.

Fixes: f16c31ccd9 ("LU-16454 mdt: Add a per-MDT "max_mod_rpcs_in_flight")
Signed-off-by: Vitaliy Kuznetsov <vkuznetsov@ddn.com>
Change-Id: I5576da1dbcaa0b4202af4b02023a46991f443a4b
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50010
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>