net: stmmac: dwmac-sun8i: Variable "val" in function sun8i_dwmac_set_syscon()...

net: stmmac: dwmac-sun8i: Variable "val" in function sun8i_dwmac_set_syscon() could be uninitialized

In function sun8i_dwmac_set_syscon(), local variable "val" could
be uninitialized if function regmap_field_read() returns -EINVAL.
However, it will be used directly in the if statement, which
is potentially unsafe.

Signed-off-by: Yizhuo <yzhai003@ucr.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>