nfp: populate MODULE_VERSION

DKMS and similar out-of-tree module replacement services use
module version to make sure the out-of-tree software is not
older than the module shipped with the kernel.  We use the
kernel version in ethtool -i output, put it into MODULE_VERSION
as well.

Reported-by: Jan Gutter <jan.gutter@netronome.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>