xfs: do not call xfs_bdstrat_cb in xfs_buf_iodone_callbacks

xfs_bdstrat_cb only adds a check for a shutdown filesystem over
xfs_buf_iorequest, but xfs_buf_iodone_callbacks just checked for a shut down
filesystem a little earlier.  In addition the shutdown handling in
xfs_bdstrat_cb is not very suitable for this caller.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>