xfs: unlock the inode before log force in xfs_change_file_space

Let the transaction commit unlock the inode before it potentially causes
a synchronous log force.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Alex Elder <aelder@sgi.com>