xfs/119: fix MKFS_OPTIONS exporting

xfs/119: fix MKFS_OPTIONS exporting

This test originally exported its own MKFS_OPTIONS to force the tested
filesystem config to the mkfs defaults + test-specific log size options.
This overrides whatever the test runner might have set in MKFS_OPTIONS.

In commit 2fd273886b525 ("xfs: refactor minimum log size formatting
code") we fail to export our test-specific MKFS_OPTIONS before
calculating the minimum log size, which leads to the wrong min log size
being calculated once we fixed the helper to be smarter about mkfs options.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>