devlink: Do not hold devlink mutex when initializing devlink fields

There is no need to hold a device global lock when initializing
devlink device fields of a devlink instance which is not yet part of the
devices list.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>