devlink: remove some unnecessary code

This code checks if (attrs[DEVLINK_ATTR_TRAP_POLICER_ID]) twice.  Once
at the start of the function and then a couple lines later.  Delete the
second check since that one must be true.

Because the second condition is always true, it means the:

	policer_item = group_item->policer_item;

assignment is immediately over-written.  Delete that as well.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/r/Y8EJz8oxpMhfiPUb@kili


Signed-off-by: Paolo Abeni <pabeni@redhat.com>