net/ethtool/ioctl: remove if n_stats checks from ethtool_get_phy_stats

Now that we always early return if we don't have any stats we can remove
these checks as they're no longer necessary.

Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>