net: pcs: lynx: check that the fwnode is available prior to use

commit  6a7b405fab0f2cc49a07d5113c8af3a53f2df25f from
https://github.com/nxp-imx/linux-imx

 lf-6.1.y

Check that the fwnode is marked as available prior to trying to lookup
the PCS device, and return -ENODEV if unavailable. Document the return
codes from lynx_pcs_create_fwnode().

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
(cherry picked from commit d143898c)
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>