net: sfp: ignore disabled SFP node

Commit ce0aa27f ("sfp: add sfp-bus to bridge between network devices
and sfp cages") added code which finds SFP bus DT node even if the node
is disabled with status = "disabled". Because of this, when phylink is
created, it ends with non-null .sfp_bus member, even though the SFP
module is not probed (because the node is disabled).

We need to ignore disabled SFP bus node.

Fixes: ce0aa27f ("sfp: add sfp-bus to bridge between network devices and sfp cages")
Signed-off-by: Marek Behún <kabel@kernel.org>
Cc: stable@vger.kernel.org # 2203cbf2 ("net: sfp: move fwnode parsing into sfp-bus layer")
Signed-off-by: David S. Miller <davem@davemloft.net>