devlink: make devlink_param_driverinit_value_set() return void

devlink_param_driverinit_value_set() currently returns int with possible
error, but no user is checking it anyway. The only reason for a fail is
a driver bug. So convert the function to return void and put WARN_ONs
on error paths.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>