net: phy: qcom: at803x: fix kernel panic with at8031_probe

In the Linux kernel, the following vulnerability has been resolved:

net: phy: qcom: at803x: fix kernel panic with at8031_probe

On reworking and splitting the at803x driver, in splitting function of at803x PHYs it was added a NULL dereference bug where priv is referenced before it's actually allocated and then is tried to write to for the is_1000basex and is_fiber variables in the case of at8031, writing on the wrong address.

Fix this by correctly setting priv local variable only after at803x_probe is called and actually allocates priv in the phydev struct.