net: phy: Use IS_ERR() to check and simplify code

Use IS_ERR() and PTR_ERR() instead of PTR_ZRR_OR_ZERO()
to simplify code, avoid redundant paramenter definitions
and judgements.

Signed-off-by: Zhang Shengju <zhangshengju@cmss.chinamobile.com>
Signed-off-by: Tang Bin <tangbin@cmss.chinamobile.com>
Signed-off-by: David S. Miller <davem@davemloft.net>