netdev: octeon_mgmt: Fix section mismatch errors.

We started getting:

WARNING: drivers/net/built-in.o(.data+0x10f0): Section mismatch in
reference from the variable octeon_mgmt_driver to the function
.init.text:octeon_mgmt_probe()

This fixes it.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>