devlink rate: Remove unnecessary 'static' from a couple places

devlink_rate_node_get_by_name() and devlink_rate_nodes_destroy() have a
couple of unnecessary static variables for iterating over devlink rates.

This could lead to races/corruption/unhappiness if two concurrent
operations execute the same function.

Remove 'static' from both. It's amazing this was missed for 4+ years.
While at it, I confirmed there are no more examples of this mistake in
net/ with 1, 2 or 3 levels of indentation.

Fixes: a8ecb93e ("devlink: Introduce rate nodes")
Signed-off-by: Cosmin Ratiu <cratiu@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>