Squashfs: fix mount time sanity check for corrupted superblock

A Squashfs filesystem containing nothing but an empty directory,
although unusual and ultimately pointless, is still valid.

The directory_table >= next_table sanity check rejects these
filesystems as invalid because the directory_table is empty and
equal to next_table.
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>

fs/squashfs/super.c

@@ -290,7 +290,7 @@ static int squashfs_fill_super(struct super_block *sb, void *data, int silent)
 
 check_directory_table:
 	/* Sanity check directory_table */
-	if (msblk->directory_table >= next_table) {
+	if (msblk->directory_table > next_table) {
 		err = -EINVAL;
 		goto failed_mount;
 	}