fs/affs/super.c: destroy sbi mutex in affs_kill_sb()

Call mutex_destroy() on superblock mutex in affs_kill_sb() otherwise mutex
debugging code isn't able to detect that mutex is used after being freed.
(thanks to Jan Kara for complete definition).
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/affs/super.c

@@ -602,6 +602,7 @@ static void affs_kill_sb(struct super_block *sb)
 		affs_free_bitmap(sb);
 		affs_brelse(sbi->s_root_bh);
 		kfree(sbi->s_prefix);
+		mutex_destroy(&sbi->s_bmlock);
 		kfree(sbi);
 	}
 }