net/nfp: Update driver to use global kernel version

Change nfp driver to use globally defined kernel version.

Reported-by: Borislav Petkov <bp@suse.de>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>