xfs: fix endian warning in xlog_recover_get_buf_lsn()

sparse reports:

fs/xfs/xfs_log_recover.c:2017:24: sparse: cast to restricted __be64

Because I used the wrong structure for the on-disk superblock cast
in 50d5c8d8 ("xfs: check LSN ordering for v5 superblocks during
recovery"). Fix it.

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

fs/xfs/xfs_log_recover.c

@@ -2014,7 +2014,7 @@ xlog_recover_get_buf_lsn(
 	case XFS_ATTR3_RMT_MAGIC:
 		return be64_to_cpu(((struct xfs_attr3_rmt_hdr *)blk)->rm_lsn);
 	case XFS_SB_MAGIC:
-		return be64_to_cpu(((struct xfs_sb *)blk)->sb_lsn);
+		return be64_to_cpu(((struct xfs_dsb *)blk)->sb_lsn);
 	default:
 		break;
 	}