e100: Cocci spatch "pool_zalloc-simple"

Use *_pool_zalloc rather than *_pool_alloc followed by memset with 0.
Found by coccinelle spatch "api/alloc/pool_zalloc-simple.cocci"

Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: David S. Miller <davem@davemloft.net>