ocfs2: remove some redundant casting

There are two standard techniques for dereferencing structures pointed
to by void *: cast to the right type each time they're used, or assign
to local variables of the right type.

But there's no need to do *both*.

Signed-off-by: George Spelvin <linux@horizon.com>
Cc: Mark Fasheh <mfasheh@suse.com>
Acked-by: Joel Becker <jlbec@evilplan.org>
Reviewed-by: Jie Liu <jeff.liu@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>