xfs: fix Sphinx documentation warning

Fix Sphinx documentation format warning by not indenting so much.

Documentation/admin-guide/xfs.rst:257: WARNING: Block quote ends without a blank line; unexpected unindent.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: linux-xfs@vger.kernel.org
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>