xfs: Fix xfs_prepare_shift() range for RT

xfs: Fix xfs_prepare_shift() range for RT

[ Upstream commit f23660f059470ec7043748da7641e84183c23bc8 ]

The RT extent range must be considered in the xfs_flush_unmap_range() call
to stabilize the boundary.

This code change is originally from Dave Chinner.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: John Garry <john.g.garry@oracle.com>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>
Signed-off-by: Leah Rumancik <leah.rumancik@gmail.com>
Acked-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>