net: bcmgenet: Fix return value check for fixed_phy_register()

stable inclusion
from stable-v5.10.193
commit 67c8d7ef54df41ef394c669fae2c26632c7a64cd
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I9399M

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=67c8d7ef54df41ef394c669fae2c26632c7a64cd



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[ Upstream commit 32bbe64a ]

The fixed_phy_register() function returns error pointers and never
returns NULL. Update the checks accordingly.

Fixes: b0ba512e ("net: bcmgenet: enable driver to work without a device tree")
Signed-off-by: Ruan Jinjie <ruanjinjie@huawei.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Acked-by: Doug Berger <opendmb@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>