net: hisilicon: Fix usage of uninitialized variable in function mdio_sc_cfg_reg_write()

[ Upstream commit 53de429f4e88f538f7a8ec2b18be8c0cd9b2c8e1 ]

In function mdio_sc_cfg_reg_write(), variable "reg_value" could be
uninitialized if regmap_read() fails. However, "reg_value" is used
to decide the control flow later in the if statement, which is
potentially unsafe.

Signed-off-by: Yizhuo <yzhai003@ucr.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>