LU-16778 tests: sanity-quota_75 fix

LU-16778 tests: sanity-quota_75 fix

Change conf=fsync to oflag=direct to avoid
cache write.

Lustre-change: https://review.whamcloud.com/51158
Lustre-commit: TBD (from b1c5e39335820602abeecbb91a3afb86879f84f2)

Test-Parameters: trivial testlist=sanity-quota env=ONLY=75,ONLY_REPEAT=100
Signed-off-by: Sergey Cheremencev <scherementsev@ddn.com>
Change-Id: Iff04bac63f772dc2d0d0ad765d210b2539fbe33e
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/51407
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>