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

stable inclusion
from stable-v5.10.193
commit 92b20b1569eb069988fb2821aeea32312774a3ce
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=92b20b1569eb069988fb2821aeea32312774a3ce



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[ Upstream commit 23a14488 ]

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

Fixes: c25b23b8 ("bgmac: register fixed PHY for ARM BCM470X / BCM5301X chipsets")
Signed-off-by: Ruan Jinjie <ruanjinjie@huawei.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Leon Romanovsky <leonro@nvidia.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>