xfs/177: force a small file system size

xfs/177: force a small file system size

This test make assumptions about the number of metadata inodes.  When
using small realtime group size (e.g. the customary 256MB for SMR
hard drives) this assumption gets violated even with modest file system
size.  Force a small file system size to side-step this issue.

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