LU-15626 tests: Fix "error" reported by shellcheck for sanity-lfsck

LU-15626 tests: Fix "error" reported by shellcheck for sanity-lfsck

This patch fixes "error" issues reported by shellcheck
for file lustre/tests/sanity-lfsck

Test-Parameters: trivial testlist=sanity-lfsck
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: I3f85cb04f93125ed132831c14a8a3f3616c99a0d
Reviewed-on: https://review.whamcloud.com/46795
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>