net: pcnet: Move initialize function at the end

Move the function at the end of the driver, so we could drop
various forward declarations later. No functional change.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>