drivers/s390/net: Drop memory allocation cast

Drop cast on the result of kmalloc and similar functions.

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

// <smpl>
@@
type T;
@@

- (T *)
  (\(kmalloc\|kzalloc\|kcalloc\|kmem_cache_alloc\|kmem_cache_zalloc\|
   kmem_cache_alloc_node\|kmalloc_node\|kzalloc_node\)(...))
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>