In case of error, the function get_phy_device() returns ERR_PTR()
and never returns NULL. The NULL test in the return value check
should be replaced with IS_ERR().

Fixes: bc93e19d ("net: ethernet: adi: Add ADIN1110 support")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20220922021023.811581-1-weiyongjun@huaweicloud.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>