xfs: fix check on struct_version for versions 4 or greater

It appears that the check for versions 4 or more is incorrect and is
off-by-one. Fix this.

Detected by CoverityScan, CID#1463775 ("Logically dead code")

Fixes: ac503a4cc9e8 ("xfs: refactor the geometry structure filling function")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/libxfs/xfs_sb.c

@@ -951,7 +951,7 @@ xfs_fs_geometry(
 	geo->rtsectsize = sbp->sb_blocksize;
 	geo->dirblocksize = xfs_dir2_dirblock_bytes(sbp);
 
-	if (struct_version < 3)
+	if (struct_version < 4)
 		return 0;
 
 	if (xfs_sb_version_haslogv2(sbp))