Fix fall out from removal of memset casts

Fix fall out from removal of memset casts

In places where we're doing pointer arithmetic, we must cast to (char
*), because pointer arithmetic on a void * isn't permitted by the C
standard. Sadly gcc lets us get away with it 'for convenience'.

Reinstate the necessary casts.

Reviewed-on: http://gerrit.openafs.org/707
Tested-by: Jeffrey Altman <jaltman@openafs.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>