net: dsa: hellcreek: Print warning only once

In case the source port cannot be decoded, print the warning only once. This
still brings attention to the user and does not spam the logs at the same time.

Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Link: https://lore.kernel.org/r/20220830163448.8921-1-kurt@linutronix.de


Signed-off-by: Jakub Kicinski <kuba@kernel.org>