xfs/185: don't use SCRATCH_{,RT}DEV helpers

xfs/185: don't use SCRATCH_{,RT}DEV helpers

This tests creates loop-based data and rt devices for testing.  Don't
override SCRATCH_{,RT}DEV and don't use the helpers based on it because
the options specified in MKFS_OPTIONS might not work for this
configuration.  This also means that we will now never use a log device
for this test even if SCRATCH_LOGDEV was set, which is fine because the
log device is not relevant for what is tested.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Zorro Lang <zlang@kernel.org>