devlink: fix the name of value arg of devl_param_driverinit_value_get()

Probably due to copy-paste error, the name of the arg is "init_val"
which is misleading, as the pointer is used to point to struct where to
store the current value. Rename it to "val" and change the arg comment
a bit on the way.

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