PCI/switchtec: Replace ENOTSUPP with EOPNOTSUPP

ENOTSUPP is not a SUSV4 error code, and the following checkpatch.pl
warning will be given for new patches which still use ENOTSUPP.

    WARNING: ENOTSUPP is not a SUSV4 error code, prefer EOPNOTSUPP

See the link below for the discussion.

  https://lore.kernel.org/netdev/20200511165319.2251678-1-kuba@kernel.org/

Replace ENOTSUPP with EOPNOTSUPP to align with future patches which will
be using EOPNOTSUPP.

Link: https://lore.kernel.org/r/20211014141859.11444-5-kelvin.cao@microchip.com


Signed-off-by: Kelvin Cao <kelvin.cao@microchip.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>