drivers:net: fix return value check in ocelot_fdma_receive_skb

ocelot_fdma_receive_skb should return false if an unexpected
value is returned by pskb_trim.

Signed-off-by: Yuanjun Gong <ruc_gongyuanjun@163.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>