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>
diff --git a/fs/affs/super.c b/fs/affs/super.c
index f754ab6..ee8eca7 100644
--- a/fs/affs/super.c
+++ b/fs/affs/super.c
@@ -602,6 +602,7 @@
 		affs_free_bitmap(sb);
 		affs_brelse(sbi->s_root_bh);
 		kfree(sbi->s_prefix);
+		mutex_destroy(&sbi->s_bmlock);
 		kfree(sbi);
 	}
 }