affs: introduce VFS superblock object back-reference

Add an 'sb' VFS superblock back-reference to the 'struct affs_sb_info' data
structure - we will need to find the VFS superblock from a 'struct
affs_sb_info' object in the next patch, so this change is jut a preparation.
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/affs/affs.h

@@ -100,6 +100,7 @@ struct affs_sb_info {
 	char *s_prefix;			/* Prefix for volumes and assigns. */
 	char s_volume[32];		/* Volume prefix for absolute symlinks. */
 	spinlock_t symlink_lock;	/* protects the previous two */
+	struct super_block *sb;		/* the VFS superblock object */
 };
 
 #define SF_INTL		0x0001		/* International filesystem. */

fs/affs/super.c

@@ -299,6 +299,7 @@ static int affs_fill_super(struct super_block *sb, void *data, int silent)
 		return -ENOMEM;
 
 	sb->s_fs_info = sbi;
+	sbi->sb = sb;
 	mutex_init(&sbi->s_bmlock);
 	spin_lock_init(&sbi->symlink_lock);