devlink: Fix param cmode driverinit for string type

Driverinit configuration mode value is held by devlink to enable the
driver fetch the value after reload command. In case the param type is
string devlink should copy the value from driver string buffer to
devlink string buffer on devlink_param_driverinit_value_set() and
vice-versa on devlink_param_driverinit_value_get().

Fixes: ec01aeb1 ("devlink: Add support for get/set driverinit value")
Signed-off-by: Moshe Shemesh <moshe@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>