net: make dev_get_port_parent_id slightly more readable

Cosmetic commit making dev_get_port_parent_id slightly more readable.
There is no need to split the condition to return after calling
devlink_compat_switch_id_get and after that 'recurse' is always true.

Signed-off-by: Antoine Tenart <atenart@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>