net: phy: sfp: clean up a condition

The acpi_node_get_property_reference() doesn't return ACPI error codes,
it just returns regular negative kernel error codes.  This patch doesn't
affect run time, it's just a clean up.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Ruslan Babayev <ruslan@babayev.com>
Signed-off-by: David S. Miller <davem@davemloft.net>