Merge branch 'fixed_phy_register-return-value'

Ruan Jinjie says:

====================
net: Fix return value check for fixed_phy_register()

The fixed_phy_register() function returns error pointers and never
returns NULL. Update the checks accordingly.

Changes in v3:
- Drop the error fix patch for fixed_phy_get_gpiod().
- Split the error code update code into another patch set as suggested.
- Update the commit title and message.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>