[S390] drivers: Correct size given to memset

Memset should be given the size of the structure, not the size of the pointer.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
type T;
T *x;
expression E;
@@

memset(x, E, sizeof(
+ *
 x))
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>