xfs/076: only create files on the data device

xfs/076: only create files on the data device

This test checks that filesystems with sparse inode support can continue
to allocate inodes when free space gets fragmented.  Inodes only exist
on the data device, so we need to ensure that realtime is not enabled on
the filesystem so that the rt metadata doesn't mess with the inode usage
percentage and cause a test failure.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>