sh_eth: Remove redundant alignment adjustment

PTR_ALIGN macro after skb_reserve is redundant, because skb_reserve
function adjusts the alignment of skb->data.

Signed-off-by: Mitsuhiro Kimura <mitsuhiro.kimura.kc@renesas.com>
Signed-off-by: Yoshihiro Kaneko <ykaneko0929@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>